{{short description|Effort to permanently eliminate all cases of poliomyelitis infection}} {{for|the vaccine|Polio vaccine}} {{Use dmy dates|date=May 2022}} {{cs1 config|name-list-style=vanc|display-authors=6}} thumb|A child receives oral polio vaccine during a 2002 campaign to immunize children in India. [[File:Polio.jpg|thumb|Poliovirus]]
<!-- Defining the topic and describing the current effort to achieve eradication. --> '''Polio eradication''', the goal of permanent global cessation of circulation of the poliovirus and hence elimination of the poliomyelitis (polio) it causes, is the aim of a multinational public health effort begun in 1988, led by the World Health Organization (WHO), the United Nations Children's Fund (UNICEF) and the Rotary Foundation.<ref>{{Cite web|title = Polio Eradication |url = http://www.globalhealthstrategies.com/issues/polio-eradication|website = Global Health Strategies | date=13 June 2011 |archive-url=https://web.archive.org/web/20160308153348/http://globalhealthstrategies.com/issues/polio-eradication |archive-date=8 March 2016 |access-date = 11 February 2016}}</ref> These organizations, along with the U.S. Centers for Disease Control and Prevention (CDC) and The Gates Foundation, have spearheaded the campaign through the Global Polio Eradication Initiative (GPEI). Successful eradication of infectious diseases has been achieved twice before, with smallpox in humans<ref name="WHO_smallpox">{{cite web |title=Smallpox [Fact Sheet] |publisher=World Health Organization (WHO) |url=https://www.who.int/mediacentre/factsheets/smallpox/en/ |archive-url=https://web.archive.org/web/20110203051426/http://www.who.int/mediacentre/factsheets/smallpox/en/ |archive-date=3 February 2011 |access-date=9 November 2013 }}</ref> and rinderpest in ruminants.<ref name="bbc">{{cite news |title=Rinderpest virus has been wiped out, scientists say |url=https://www.bbc.co.uk/news/science-environment-11542653 |publisher=BBC News Online |date=14 October 2010 |access-date=14 October 2010 | vauthors = Ghosh P |archive-date=3 May 2019 |archive-url=https://web.archive.org/web/20190503022917/https://www.bbc.co.uk/news/science-environment-11542653 |url-status=live }}</ref>
<!-- The means by which eradication is attempted (i.e. vaccination). --> Prevention of disease spread is accomplished by vaccination. There are two kinds of polio vaccine—oral polio vaccine (OPV), which uses weakened poliovirus, and inactivated polio vaccine (IPV), which is injected. OPV is less expensive and easier to administer, and can spread immunity beyond the person vaccinated, creating contact immunity. It has been the predominant vaccine used. However, under conditions of long-term vaccine virus circulation in under-vaccinated populations, mutations can reactivate the virus to produce a polio-inducing strain, while OPV can also, in rare circumstances, induce polio or persistent asymptomatic infection in vaccinated individuals, particularly those who are immunodeficient. IPV, being inactivated, does not carry these risks, but does not induce contact immunity. IPV is more costly and the logistics of its delivery are more challenging.
<!-- Progress thus far. --> Nigeria is the latest country to have officially stopped endemic transmission of wild poliovirus, with its last reported case in 2016.<ref name="Scherbel-Ball_2020" /> Of the three strains of WPV, the last recorded wild case caused by type{{nbsp}}2 (WPV2) was in 1999, and WPV2 was declared eradicated in 2015. Type{{nbsp}}3 (WPV3) is last known to have caused polio in 2012, and was declared eradicated in 2019.<ref name="polioeradication.org">{{Cite web |title=GPEI-Two out of three wild poliovirus strains eradicated |url=http://polioeradication.org/news-post/two-out-of-three-wild-poliovirus-strains-eradicated/ |archive-url=https://web.archive.org/web/20191107080405/http://polioeradication.org/news-post/two-out-of-three-wild-poliovirus-strains-eradicated/ |archive-date=7 November 2019 |access-date=2 November 2019}}</ref> All wild-virus cases since that date have been due to type{{nbsp}}1 (WPV1).<ref name="Geiger_2024">{{cite journal | vauthors = Geiger K, Stehling-Ariza T, Bigouette JP, Bennett SD, Burns CC, Quddus A, Wassilak SG, Bolu O | title = Progress Toward Poliomyelitis Eradication - Worldwide, January 2022-December 2023 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 73 | issue = 19 | pages = 441–446 | date = May 2024 | pmid = 38753550 | pmc = 11115430 | doi = 10.15585/mmwr.mm7319a4 | url = }}</ref>
<!-- Continuing cases --> Currently, Afghanistan and Pakistan are the only two countries where the disease is still classified as endemic.<ref>{{cite web |title=Endemic Countries - GPEI |url=http://polioeradication.org/where-we-work/polio-endemic-countries/ |url-status=live |archive-url=https://web.archive.org/web/20200722124813/http://polioeradication.org/where-we-work/polio-endemic-countries/ |archive-date=22 July 2020 |access-date=17 July 2020}}</ref><ref>{{Cite web |title=Poliomyelitis (polio) |url=https://www.who.int/westernpacific/health-topics/poliomyelitis |url-status=live |archive-url=https://web.archive.org/web/20200728014939/https://www.who.int/westernpacific/health-topics/poliomyelitis |archive-date=28 July 2020 |access-date=2020-08-28 |website=www.who.int |language=en}}</ref> Recent polio cases arise from two sources, the original "wild" poliovirus (WPV), and the much more prevalent mutated oral vaccine strains, known as circulating vaccine-derived poliovirus (cVDPV) or variant poliovirus. Vaccines against each of the three wild strains of polio have given rise to strains of cVDPV, with cVDPV2 being most prominent. cVDPV caused 312 confirmed paralytic polio cases worldwide in 2024, and was detected in 21 countries.<ref name="WPVcurrent">{{cite web |date=2025-07-14 |title=Global Wild Acute Flaccid Paralysis (AFP) cases and environmental samples 2018 - 2025 |url=https://polioeradication.org/wild-poliovirus-count/ |access-date=2025-07-17 |website=Global Polio Eradication Initiative - World Health Organization}}</ref><ref name="VDPVcurrent">{{cite web |date=2025-07-14 |title=Global Circulating Vaccine-derived Poliovirus (cVDPV) - Acute Flaccid Paralysis (AFP) cases and environmental samples 2021-2025 |url=https://polioeradication.org/circulating-vaccine-derived-poliovirus-count/ |access-date=2025-07-17 |website=Global Polio Eradication Initiative - World Health Organization}}</ref>
== Factors influencing eradication of polio == Eradication of polio has been defined in various ways:
# As elimination of the occurrence of poliomyelitis even in the absence of human intervention.<ref name="Barrett">{{cite journal | vauthors = Barrett S | title = Eradication versus control: the economics of global infectious disease policies | journal = Bulletin of the World Health Organization | volume = 82 | issue = 9 | pages = 683–688 | date = September 2004 | pmid = 15628206 | pmc = 2622975 | hdl = 10665/269225 }}</ref> # As extinction of poliovirus, such that the infectious agent no longer exists in nature or in the laboratory.<ref>{{cite journal | vauthors = Cockburn TA | title = Eradication of infectious diseases | journal = Science | volume = 133 | issue = 3458 | pages = 1050–1058 | date = April 1961 | pmid = 13694225 | doi = 10.1126/science.133.3458.1050 | bibcode = 1961Sci...133.1050C }}</ref> # As control of an infection to the point at which transmission of the disease ceased within a specified area.<ref name="Barrett" /> # As reduction of the worldwide incidence of poliomyelitis to zero as a result of deliberate efforts, and requiring no further control measures.<ref>{{cite journal | vauthors = | title = Recommendations of the International Task Force for Disease Eradication | journal = MMWR. Recommendations and Reports | volume = 42 | issue = RR-16 | pages = 1–38 | date = December 1993 | pmid = 8145708 | url = https://www.cdc.gov/mmwr/PDF/rr/rr4216.pdf | access-date = 27 October 2019 | url-status = live | archive-url = https://web.archive.org/web/20200529232511/https://www.cdc.gov/mmwr/PDF/rr/rr4216.pdf | archive-date = 29 May 2020 }}</ref>
In theory, if the right tools were available, it would be possible to eradicate all infectious diseases that reside only in a human host. In reality, there are distinct biological features of the organisms and technical factors of dealing with them that make their potential eradicability more or less likely. Three indicators, however, are considered of primary importance in determining the likelihood of successful eradication: that effective interventional tools are available to interrupt transmission of the agent, such as a vaccine; that diagnostic tools, with sufficient sensitivity and specificity, be available to detect infections that can lead to transmission of the disease; and that humans are required for the life-cycle of the agent, which has no other vertebrate reservoir and cannot amplify in the environment.<ref>{{cite journal | title = Global Disease Elimination and Eradication as Public Health Strategies. Proceedings of a conference. Atlanta, Georgia, USA. 23-25 February 1998. | journal = MMWR Supplements | volume = 48 | pages = 1–208 | date = December 1999 | pmid = 11186140 | url = https://www.cdc.gov/mmwr/pdf/other/mm48SU01.pdf | access-date = 27 October 2019 | url-status = live | archive-url = https://web.archive.org/web/20190508001201/https://www.cdc.gov/mmwr/pdf/other/mm48su01.pdf | archive-date = 8 May 2019 | author1 = Centers for Disease Control and Prevention (CDC) }}</ref>
=== Strategy === The most important step in eradication of polio is interruption of endemic transmission of poliovirus. Stopping polio transmission has been pursued through a combination of routine immunization, supplementary immunization campaigns, and surveillance of possible outbreaks. Several key strategies have been outlined for stopping polio transmission:<ref>{{cite book | vauthors = ((Global Polio Eradication Initiative)), ((World Health Organization)) | title = Global polio eradication initiative: strategic plan 2004–2008 | publisher = World Health Organization (WHO) | year = 2003 | location = Geneva | url = http://apps.who.int/iris/bitstream/10665/42850/1/924159117X.pdf | isbn = 978-92-4-159117-1 | hdl = 10665/42850 | access-date = 26 October 2019 | archive-date = 20 August 2017 | archive-url = https://web.archive.org/web/20170820152532/http://apps.who.int/iris/bitstream/10665/42850/1/924159117X.pdf | url-status = live }}</ref>
# High infant immunization coverage with four doses of oral polio vaccine (OPV) in the first year of life in developing and endemic countries, and routine immunization with OPV or IPV elsewhere. # Organization of "national immunization days" to provide supplementary doses of oral polio vaccine to all children less than five years old. # Active surveillance for poliovirus through reporting and laboratory testing of all cases of acute flaccid paralysis. Acute flaccid paralysis (AFP) is a clinical manifestation of poliomyelitis characterized by weakness or paralysis and reduced muscle tone without other obvious cause (e.g., trauma) among children less than fifteen years old. Other pathogenic agents can also cause AFP, such as enteroviruses, echoviruses, and adenoviruses.<ref>{{cite web | title = Acute Flaccid Paralysis (AFP) | work = Public Health Notifiable Disease Management Guidelines | publisher = Alberta Government Health and Wellness | year = 2018 | url = https://open.alberta.ca/publications/acute-flaccid-paralysis-afp | access-date = 28 October 2019 | archive-date = 28 October 2019 | archive-url = https://web.archive.org/web/20191028190537/https://open.alberta.ca/publications/acute-flaccid-paralysis-afp | url-status = live }}</ref> # Expanded environmental surveillance to detect the presence of poliovirus in communities.<ref name="surveillance">{{cite report |vauthors=((Global Polio Eradication Initiative)), ((World Health Organization)) |title=Polio environmental surveillance expansion plan: global expansion plan under the endgame strategy 2013-2018 |publisher=World Health Organization (WHO) |date=April 2015 |access-date=1 July 2018 |url=http://polioeradication.org/wp-content/uploads/2016/07/GPLN_ExpansionPlanES.pdf |hdl=10665/276245 |id=WHO/POLIO/15.02 |archive-date=20 June 2017 |archive-url=https://web.archive.org/web/20170620180847/http://polioeradication.org/wp-content/uploads/2016/07/GPLN_ExpansionPlanES.pdf |url-status=live }}</ref> Sewage samples are collected at regular and random sites and tested in laboratories for the presence of WPV or cVDPV. Since most polio infections are asymptomatic, transmission can occur in spite of the absence of polio-related AFP cases, and such monitoring helps to evaluate the degree to which virus continues to circulate in an area. # Targeted "mop-up" campaigns once poliovirus transmission is limited to specific geographical foci.
=== Vaccination === thumb|Somali boy receiving injection of inactivated polio vaccine (IPV) There are two distinct types of polio vaccine. Oral polio vaccine (OPV, or Sabin vaccine) contains attenuated poliovirus.<ref name="GPEI-OPV">{{cite web |title=OPV - Oral Polio Vaccine |url=https://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ |access-date=9 August 2024 |website=Global Polio Eradication Initiative (GPEI) |publisher= |archive-date=30 March 2024 |archive-url=https://web.archive.org/web/20240330195829/https://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ |url-status=dead }}</ref> OPV is delivered as oral drops or infused into sugar cubes. It is highly effective and inexpensive (about {{US$|0.15 to 0.20}} per dose in 2024<ref name="GPEI-OPV" />) and its availability has bolstered efforts to eradicate polio. The vaccine confers long-term, possibly lifelong, immunity to the virus.<ref>{{cite journal | vauthors = Larocca AM, Bianchi FP, Bozzi A, Tafuri S, Stefanizzi P, Germinario CA | title = Long-Term Immunogenicity of Inactivated and Oral Polio Vaccines: An Italian Retrospective Cohort Study | journal = Vaccines | volume = 10 | issue = 8 | pages = 1329 | date = August 2022 | pmid = 36016217 | pmc = 9413249 | doi = 10.3390/vaccines10081329 | doi-access = free }}</ref> Because of its route of administration, it induces an immunization of the intestinal mucosa that protects against subsequent infection, though multiple doses are necessary to achieve effective prophylaxis.<ref name="GPEI-OPV" /> Attenuated poliovirus derived from the oral polio vaccine is excreted, infecting and indirectly inducing immunity in unvaccinated individuals, and thus amplifying the effects of the doses delivered.<ref name= Nathan>{{cite journal | vauthors = Nathanson N, Martin JR | title = The epidemiology of poliomyelitis: enigmas surrounding its appearance, epidemicity, and disappearance | journal = American Journal of Epidemiology | volume = 110 | issue = 6 | pages = 672–692 | date = December 1979 | pmid = 400274 | doi = 10.1093/oxfordjournals.aje.a112848 }}</ref> The oral administration does not require special medical equipment or training. Taken together, these advantages have made it the favored vaccine of many countries, and it has long been preferred by the global eradication initiative.<ref name="GPEI-OPV" />
The primary disadvantage of OPV derives from its inherent nature. As an attenuated but active virus, it can induce vaccine-associated paralytic poliomyelitis (VAPP) in approximately one individual per every 2.7{{nbsp}}million doses administered.<ref name="GPEI-OPV" /> The live virus can circulate in under-vaccinated populations (circulating vaccine-derived poliovirus, cVDPV) and over time can mutate to a neurovirulent form causing paralytic polio.<ref name="GPEI-OPV" /> Until recent times, a trivalent OPV containing all three virus strains was used, but with the eradication of wild poliovirus type{{nbsp}}2 this was phased out in 2016 and replaced with bivalent vaccine containing just types 1 and 3, supplemented with monovalent type{{nbsp}}2 OPV in regions with documented cVDPV2 circulation.<ref name="GPEI-OPV" /> A novel OPV2 vaccine (nOPV2) genetically modified to reduce the likelihood of disease-causing activating mutations was granted emergency licencing in 2021, and subsequently full licensure in December 2023.<ref name=":x2">{{Cite web |date=12 April 2024 |title=GPEI-OPV Oral polio vaccine |url=https://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ |access-date=12 April 2024 |website=Global Polio Eradication Initiative - World Health Organization |language=en-GB |archive-date=30 March 2024 |archive-url=https://web.archive.org/web/20240330195829/https://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ |url-status=dead }}</ref> Genetically stabilsed vaccines targeting poliovirus types 1 and 3 are in development, with the intention that these will eventually completely replace the Sabin vaccines.<ref>{{Cite web |last=Gadye |first=Levi |date=2023-06-14 |title=Two New Vaccines Join the Fight to Eradicate Polio {{!}} UC San Francisco |url=https://www.ucsf.edu/news/2023/06/425601/two-new-vaccines-join-fight-eradicate-polio |access-date=2024-08-10 |website=The University of California San Francisco |language=en}}</ref>
The inactivated polio vaccine (IPV, or Salk) contains trivalent fully inactivated virus, administered by injection. This vaccine cannot induce VAPP nor do cVDPV strains arise from it, but it likewise cannot induce contact immunity and thus must be administered to every individual. Added to this are greater logistical challenges. Though a single dose is sufficient for protection, administration requires medically trained vaccinators armed with single-use needles and syringes. Taken together, these factors result in substantially higher delivery costs.<ref name="GPEI-IPV">{{cite web | url=http://polioeradication.org/polio-today/polio-prevention/the-vaccines/ipv/ | title=IPV | publisher=Global Polio Eradication Initiative (GPEI) | access-date=7 July 2018 | archive-date=28 June 2018 | archive-url=https://web.archive.org/web/20180628195559/http://polioeradication.org/polio-today/polio-prevention/the-vaccines/ipv/ | url-status=live }}</ref> Original protocols involved intramuscular injection in the arm or leg, but recently subcutaneous injection using a lower dose (so-called fractional-dose IPV, fIPV) has been found to be effective, lowering costs and also allowing for more convenient and cost-effective delivery systems.<ref name="Bahl">{{cite journal | vauthors = Bahl S, Verma H, Bhatnagar P, Haldar P, Satapathy A, Kumar KN, Horton J, Estivariz CF, Anand A, Sutter R | title = Fractional-Dose Inactivated Poliovirus Vaccine Immunization Campaign - Telangana State, India, June 2016 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 65 | issue = 33 | pages = 859–863 | date = August 2016 | pmid = 27559683 | doi = 10.15585/mmwr.mm6533a5 | url = https://www.cdc.gov/mmwr/volumes/65/wr/pdfs/mm6533.pdf | access-date = 27 October 2019 | url-status = live | doi-access = free | archive-url = https://web.archive.org/web/20171123042718/https://www.cdc.gov/mmwr/volumes/65/wr/pdfs/mm6533.pdf | archive-date = 23 November 2017 }}</ref><ref>{{cite journal | vauthors = Okayasu H, Sein C, Chang Blanc D, Gonzalez AR, Zehrung D, Jarrahian C, Macklin G, Sutter RW | title = Intradermal Administration of Fractional Doses of Inactivated Poliovirus Vaccine: A Dose-Sparing Option for Polio Immunization | journal = The Journal of Infectious Diseases | volume = 216 | issue = suppl_1 | pages = S161–S167 | date = July 2017 | pmid = 28838185 | pmc = 5853966 | doi = 10.1093/infdis/jix038 | url = https://www.who.int/immunization/sage/meetings/2017/october/7_polio_Okayasu_JID2017.pdf | access-date = 7 July 2018 | url-status = live | archive-url = https://web.archive.org/web/20200827134003/https://www.who.int/immunization/sage/meetings/2017/october/7_polio_Okayasu_JID2017.pdf | archive-date = 27 August 2020 }}</ref> The use of IPV results in serum immunity, but no intestinal immunity arises. As a consequence, vaccinated individuals are protected from contracting polio, but their intestinal mucosa may still be infected and serve as a reservoir for the excretion of live virus. For this reason, IPV is ineffective at halting ongoing outbreaks of WPV or cVDPV, but it has become the vaccine of choice for industrialized, polio-free countries.<ref name="GPEI-IPV" />
While IPV does not itself induce mucosal immunity, it has been shown to boost the mucosal immunity from OPV,<ref>{{cite journal | vauthors = Parker EP, Molodecky NA, Pons-Salort M, O'Reilly KM, Grassly NC | title = Impact of inactivated poliovirus vaccine on mucosal immunity: implications for the polio eradication endgame | journal = Expert Review of Vaccines | volume = 14 | issue = 8 | pages = 1113–1123 | year = 2015 | pmid = 26159938 | pmc = 4673562 | doi = 10.1586/14760584.2015.1052800 }}</ref> and the WHO now favors a combined protocol. It is recommended that vulnerable children receive a dose of OPV at birth, then beginning at the age of six weeks a 'primary series' consisting of three OPV doses at least four weeks apart, along with one dose of IPV after 14 weeks.<ref name="WHO-polio vaccine">{{cite web |title=International travel and health: Poliomyelitis (Polio) |url=https://www.who.int/ith/vaccines/polio/en/ |archive-url=https://web.archive.org/web/20180624181459/http://www.who.int/ith/vaccines/polio/en/ |archive-date=24 June 2018 |access-date=7 July 2018 |publisher=World Health Organization (WHO)}}</ref> This combined IPV/OPV approach has also been used in outbreak suppression.<ref>{{cite news | vauthors = Branswell H | title=Combination of oral, injectable polio vaccine used for first time in outbreak | date=20 March 2014 | access-date=7 July 2018 | publisher=CTV | url=https://www.ctvnews.ca/health/article/combination-of-oral-injectable-polio-vaccine-used-for-first-time-in-outbreak/ | archive-date=8 July 2018 | archive-url=https://web.archive.org/web/20180708015903/https://www.ctvnews.ca/health/combination-of-oral-injectable-polio-vaccine-used-for-first-time-in-outbreak-1.1738666 | url-status=live }}</ref>
==== Herd immunity ==== thumb|Herd Immunity vs Without Herd Immunity Polio vaccination is also important in the development of herd immunity.<ref name= Fine>{{cite journal | vauthors = Fine PE | title = Herd immunity: history, theory, practice | journal = Epidemiologic Reviews | volume = 15 | issue = 2 | pages = 265–302 | year = 1993 | pmid = 8174658 | doi = 10.1093/oxfordjournals.epirev.a036121 | url = https://op12no2.me/stuff/herdhis.pdf | access-date = 27 August 2020 | url-status = live | archive-url = https://web.archive.org/web/20200709224214/https://op12no2.me/stuff/herdhis.pdf | archive-date = 9 July 2020 }}</ref> For polio to occur in a population, there must be an infecting organism (poliovirus), a susceptible human population, and a cycle of transmission. There is no animal reservoir for poliovirus, and the transmission cycle of polio is from one infected person to another person susceptible to the disease, usually through the fecal-oral route.<ref name= Nathan/> If the vast majority of the population is immune to a particular agent, the ability of that pathogen to infect another host is reduced; the cycle of transmission is interrupted, and the pathogen cannot reproduce and dies out. This concept, called community immunity or herd immunity, is important to disease eradication, because it means that it is not necessary to inoculate 100% of the population—a goal that is often logistically very difficult—to achieve the desired result. If the number of susceptible individuals can be reduced to a sufficiently small number through vaccination, then the pathogen will eventually die off.<ref>{{cite journal | vauthors = Shaw L, Spears W, Billings L, Maxim P | title = Effective Vaccination Policies | journal = Information Sciences | volume = 180 | issue = 19 | pages = 3728–3744 | date = October 2010 | pmid = 21057602 | pmc = 2967767 | doi = 10.1016/j.ins.2010.06.005 }}</ref>
Herd immunity is an important supplement to vaccination. According to the concept of herd immunity, the population for whom the vaccine fails is still protected by the immunity of those around them, and it can only be achieved when vaccination levels are high. It is estimated that the minimum herd immunity threshold for poliovirus eradication ranges from approximately 75% in wealthy high-hygiene populations to 97% in poorer environments. If routine immunization were to be stopped, the number of unvaccinated, susceptible individuals would soon exceed the capability of herd immunity to protect them.<ref>{{Cite journal |last=Fine |first=Paul E. M. |date=March 2024 |title=Population Immunity and Polio Eradication |journal=Pathogens |language=en |volume=13 |issue=3 |page=183 |doi=10.3390/pathogens13030183 |doi-access=free |issn=2076-0817 |pmc=10974847 |pmid=38535527}}</ref>
==== Vaccine-derived poliovirus ==== {{multiple image | direction = vertical | width = 300 | image1 = Poliomyelitis reported cases by year.svg | caption1 = Number of wild poliovirus cases, 1975–2024<br />(before 2000 may include small numbers of cVDPV cases) | image2 = Number of cVDPV cases.svg | caption2 = Number of cVDPV cases, 2000–2024 | align = | total_width = | alt1 = }}
While vaccination has played an instrumental role in the reduction of polio cases worldwide, the use of attenuated virus in the oral vaccine carries with it an inherent risk. The oral vaccine is a powerful tool in fighting polio in part because of its person-to-person transmission and resulting contact immunity. However, under conditions of long-term circulation in undervaccinated populations, the virus can accumulate mutations that reverse the attenuation and result in vaccine virus strains that themselves cause polio. As a result of such circulating vaccine-derived poliovirus (cVDPV) strains, polio outbreaks have periodically recurred in regions that have long been free of the wild virus, but where vaccination rates have fallen. Oral vaccines can also give rise to persistent infection in immunodeficient individuals, with the virus eventually mutating into a more virulent immunodeficiency-associated vaccine-derived poliovirus (iVDPV). In particular, the type{{nbsp}}2 strain seems prone to reversions, so in 2016 the eradication effort abandoned the trivalent oral vaccine containing attenuated strains of all three virus types and replaced it with a bivalent oral vaccine lacking the type{{nbsp}}2 virus, while a separate monovalent type{{nbsp}}2 vaccine (mOPV2) was to be used only to target existing cVDPV2 outbreaks. A novel oral vaccine targeting type{{nbsp}}2 (nOPV2) that has been genetically stabilized to make it less prone to give rise to circulating vaccine-derived strains received full licensure in December 2023, with similar vaccines targeting types 1 and 3 undergoing clinical trials.<ref>{{Cite web |last=Gadye |first=Levi |date=2023-06-14 |title=Two New Vaccines Join the Fight to Eradicate Polio |url=https://www.ucsf.edu/news/2023/06/425601/two-new-vaccines-join-fight-eradicate-polio |access-date=2024-08-10 |website=The University of California San Francisco |language=en}}</ref><ref>{{Cite journal |last1=Yeh |first1=Ming Te |last2=Bujaki |first2=Erika |last3=Dolan |first3=Patrick T. |last4=Smith |first4=Matthew |last5=Wahid |first5=Rahnuma |last6=Konz |first6=John |last7=Weiner |first7=Amy J. |last8=Bandyopadhyay |first8=Ananda S. |last9=Van Damme |first9=Pierre |last10=De Coster |first10=Ilse |last11=Revets |first11=Hilde |last12=Macadam |first12=Andrew |last13=Andino |first13=Raul |date=13 May 2020 |title=Engineering the Live-Attenuated Polio Vaccine to Prevent Reversion to Virulence |journal=Cell Host & Microbe |language=en |volume=27 |issue=5 |pages=736–751.e8 |doi=10.1016/j.chom.2020.04.003 |pmc=7566161 |pmid=32330425}}</ref> Eradication efforts will eventually require all oral vaccination to be discontinued in favor of the use of injectable vaccines. These vaccines are more expensive and more difficult to deliver, and they lack the ability to induce contact immunity because they contain only killed virus, but they likewise are incapable of giving rise to vaccine-derived viral strains.<ref>{{cite web|title=Vaccine-Derived Poliovirus|publisher=Global Polio Eradication Initiative (GPEI)|access-date=26 June 2018|url=http://polioeradication.org/polio-today/polio-prevention/the-virus/vaccine-derived-polio-viruses/|archive-date=26 June 2018|archive-url=https://web.archive.org/web/20180626025107/http://polioeradication.org/polio-today/polio-prevention/the-virus/vaccine-derived-polio-viruses/|url-status=live}}</ref><ref>{{cite journal | vauthors = Duintjer Tebbens RJ, Thompson KM | title = Managing the risk of circulating vaccine-derived poliovirus during the endgame: oral poliovirus vaccine needs | journal = BMC Infectious Diseases | volume = 15 | article-number = 390 | date = September 2015 | pmid = 26404780 | pmc = 4582727 | doi = 10.1186/s12879-015-1114-6 | doi-access = free }}</ref>
=== Surveillance === A global program of surveillance for the presence of polio and the poliovirus plays a critical role in assessment of eradication and in outbreak detection and response. Two distinct methods are used in tandem: acute flaccid paralysis (AFP) surveillance and environmental surveillance.<ref name="surv" />
Monitoring for AFP aims at identifying outbreaks of polio by screening patients displaying symptoms consistent with, but not exclusive to, severe poliovirus infection. Stool samples are collected from children presenting with AFP and evaluated for the presence of poliovirus by accredited laboratories in the Global Polio Laboratory Network. Since rates of non-polio AFP are expected to be constant and large compared to the number of polio cases, the frequency of non-polio AFP reported in a population is indicative of the effectiveness of surveillance, as is the proportion of AFP patients from whom high-quality stool samples are collected and tested, with a target of at least 80%.<ref name="surv">{{cite journal | vauthors = Patel JC, Diop OM, Gardner T, Chavan S, Jorba J, Wassilak SG, Ahmed J, Snider CJ | title = Surveillance to Track Progress Toward Polio Eradication - Worldwide, 2017-2018 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 68 | issue = 13 | pages = 312–318 | date = April 2019 | pmid = 30946737 | pmc = 6611474 | doi = 10.15585/mmwr.mm6813a4 | url = https://www.cdc.gov/mmwr/volumes/68/wr/pdfs/mm6813-H.pdf#page=16 | access-date = 27 October 2019 | url-status = live | archive-url = https://web.archive.org/web/20200826054346/https://www.cdc.gov/mmwr/volumes/68/wr/pdfs/mm6813-H.pdf#page=16 | archive-date = 26 August 2020 }}</ref>
Environmental surveillance is used to supplement AFP surveillance. This entails the routine testing of sewage samples for the presence of virus, which not only allows the effectiveness of vaccination efforts to be evaluated in countries with active transmission, but also allows the detection of new outbreaks in countries without known transmission. In 2018, the GPEI conducted environmental surveillance in 44 countries, 24 of which are in Africa.<ref name="surv" />
=== Obstacles ===
Among the greatest obstacles to global polio eradication are the lack of basic health infrastructure, which limits vaccine distribution and delivery, the crippling effects of civil war and internal strife, and the sometimes oppositional stance that marginalized communities take against what is perceived as a potentially hostile intervention by outsiders. Another challenge has been maintaining the potency of live (attenuated) vaccines in extremely hot or remote areas. The oral polio vaccine must be kept at {{convert|2|to|8|C|F}} for vaccination to be successful.<ref name="Watch">{{cite web | vauthors = Mastny L |date=25 January 1999 |title=Eradicating Polio: A Model for International Cooperation |url=http://www.worldwatch.org/node/1644 |archive-url=https://web.archive.org/web/20060608165205/http://www.worldwatch.org/node/1644 |archive-date=8 June 2006 |access-date=2 February 2007 |publisher=Worldwatch Institute}}</ref>
An independent evaluation of obstacles to polio eradication requested by the WHO and conducted in 2009 considered the major obstacles in detail by country. In Afghanistan and Pakistan, the researchers concluded that the most significant barrier was insecurity, but that managing human resources, political pressures, the movement of large populations between and within both countries, and inadequately resourced health facilities also posed problems, as did technical issues with the vaccine. In India, the major challenge appeared to be the high efficiency of transmission within the populations of Bihar and Uttar Pradesh states, set against the low (~80% after three doses against type{{nbsp}}1) seroconversion response seen from the vaccine. In Nigeria, the most critical barriers identified were management issues, in particular the highly variable importance ascribed to polio by different authorities at the local government level, although funding issues, community perceptions of vaccine safety, inadequate mobilisation of community groups, and issues with the cold chain also played a role. In those countries where international spread from endemic countries had resulted in the reestablishment of transmission, namely Angola, Chad, and South Sudan, the key issues identified were underdeveloped health systems and low routine vaccine coverage, although the low level of resources committed to Angola and South Sudan for the purpose of curtailing the spread of polio and climatic factors was also identified as playing a role.<ref name=evaluation>{{cite web|title=Polio Eradication Evaluation |url=http://www.polioeradication.org/content/general/Polio_Evaluation_Report.asp |access-date=19 February 2008 |archive-url=https://web.archive.org/web/20100706172238/http://www.polioeradication.org/content/general/Polio_Evaluation_Report.asp |archive-date=6 July 2010 }}</ref>
Two additional challenges are found in unobserved polio transmission and in vaccine-derived poliovirus. First, most individuals infected with poliovirus are asymptomatic or exhibit minor symptoms, with fewer than 1% of infections leading to paralysis,<ref>{{cite web |title=Poliomyelitis |publisher=World Health Organization (WHO) |url=https://www.who.int/biologicals/areas/vaccines/poliomyelitis/en/ |access-date=28 October 2016 |archive-date=24 October 2016 |archive-url=https://web.archive.org/web/20161024022827/http://www.who.int/biologicals/areas/vaccines/poliomyelitis/en/ }}</ref> and most infected people are unaware that they carry the disease, allowing polio to spread widely before cases are seen.<ref>{{Cite web |title=Polio and Prevention |url=http://www.polioeradication.org/Polioandprevention.aspx |website=Global Polio Eradication Initiative (GPEI) |access-date=13 September 2015 |archive-url=https://web.archive.org/web/20150907175552/http://www.polioeradication.org/Polioandprevention.aspx |archive-date=7 September 2015 }}</ref> In 2000, using new screening techniques for the molecular characterization of outbreak viral strains, it was discovered that some of the outbreaks were actually caused by circulating vaccine-derived poliovirus, following mutations or recombinations in the attenuated strain used for the oral polio vaccine. This discovery altered the strategy for the discontinuation of vaccination following polio eradication,<ref>{{cite journal | vauthors = Pallansch MA | title = Ending Use of Oral Poliovirus Vaccine - A Difficult Move in the Polio Endgame | journal = The New England Journal of Medicine | volume = 379 | issue = 9 | pages = 801–803 | date = August 2018 | pmid = 30157390 | pmc = 8083018 | doi = 10.1056/NEJMp1808903 | doi-access = free }}</ref> necessitating an eventual switch to the more expensive and logistically more problematic inactivated polio vaccine, as continued use of the oral inactivated virus would continue to produce such revertant infection-causing strains.<ref name=bumpyroad>{{cite journal | vauthors = Modlin JF | title = The bumpy road to polio eradication | journal = The New England Journal of Medicine | volume = 362 | issue = 25 | pages = 2346–2349 | date = June 2010 | pmid = 20573922 | doi = 10.1056/nejmp1005405 | doi-access = free }}</ref> The risk of vaccine-derived polio will persist long after the switch to inactivated vaccine, as a small number of chronic excretors continue to produce active virus for years (or even decades) after their initial exposure to the oral vaccine.<ref>{{cite journal | vauthors = Diop OM, Burns CC, Sutter RW, Wassilak SG, Kew OM | title = Update on Vaccine-Derived Polioviruses - Worldwide, January 2014-March 2015 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 64 | issue = 23 | pages = 640–646 | date = June 2015 | pmid = 26086635 | pmc = 4584736 | url = https://www.cdc.gov/mmwr/pdf/wk/mm6423.pdf | access-date = 27 October 2019 | url-status = live | archive-url = https://web.archive.org/web/20200629115554/https://www.cdc.gov/mmwr/pdf/wk/mm6423.pdf | archive-date = 29 June 2020 }}</ref>
In a 2012 interview with Pakistani newspaper ''Dawn'', Dr. Hussain A. Gezari, the WHO's special envoy on global polio eradication and primary healthcare, gave his views on obstacles to eradication. He said that the biggest hurdle preventing Pakistan from becoming polio-free was holding district health officials properly accountable—in national eradication campaigns officials had hired their own relatives, even young children. Gezari asked, "How do you expect a seven-year-old thumb-sucking kid to implement a polio campaign of the government?" and added that, in spite of this, "the first national campaign was initiated by your government in 1994 and that year Pakistan reported 25,000 polio cases, and the number was just 198 last year, which clearly shows that the programme is working."<ref name="WHO rejects rumours"/>
====Opposition to vaccination efforts==== {{see also|Antivaccination}} One factor contributing to the continued circulation of polio immunization programs has been opposition to vaccination in some countries.<ref name="Religious opposition"/> In one country, Pakistan, "more than 200 polio team workers" have been killed (team members include not only vaccinators but police and security personnel) from "targeted killing and terrorism" while working on polio campaigns<ref name="History-APJPH-2023">{{cite journal | vauthors = Wahid B, Kumari B, Saifullah KM, Idrees M | title = The History and Current Killings of Polio Vaccinators in Pakistan: A Need for Targeted Surveillance Strategy | journal = Asia-Pacific Journal of Public Health | volume = 35 | issue = 2–3 | pages = 183–188 | date = March 2023 | pmid = 36856226 | pmc = 10185917 | doi = 10.1177/10105395231158866 }}</ref> (the killers motivated by the belief, spread by "radical clerics", that the vaccine is part of "a Western plot to sterilize Muslims").<ref>{{cite journal | vauthors = Yusufzai A | title = Health workers murdered as Pakistan vaccinates 8.4 million children | journal = CMAJ | volume = 186 | issue = 9 | pages = E302 | date = June 2014 | pmid = 24756620 | pmc = 4050009 | doi = 10.1503/cmaj.109-4776 }}</ref>
In the context of the United States invasion of Afghanistan and the subsequent 2003 invasion of Iraq, rumours arose in the Muslim world that immunization campaigns were using intentionally-contaminated vaccines to sterilize local Muslim populations or to infect them with HIV. In Nigeria these rumours fit in with a longstanding suspicion of modern biomedicine, which since its introduction during the era of colonialism has been viewed as a projection of the power of western nations. Even before the implementation of the Global Polio Eradication Initiative, many Nigerians believed that the EPI vaccine contained fertility control drugs.<ref>{{Cite journal |last=Renne |first=Elisha |date=2006 |title=Perspectives on polio and immunization in Northern Nigeria |url=https://pubmed.ncbi.nlm.nih.gov/16765498 |journal=Social Science & Medicine (1982) |volume=63 |issue=7 |pages=1857–1869 |doi=10.1016/j.socscimed.2006.04.025 |issn=0277-9536 |pmid=16765498}}</ref> Refusal of vaccination came to be viewed as resistance to western expansionism, and when the contamination rumours led the Nigerian Supreme Council for Sharia to call for a region-wide boycott of polio vaccination, polio cases in the country increased more than five-fold between 2002 and 2006, with the uncontrolled virus then spreading across Africa and globally.<ref name=Ghani>{{cite journal | vauthors = Ghinai I, Willott C, Dadari I, Larson HJ | title = Listening to the rumours: what the northern Nigeria polio vaccine boycott can tell us ten years on | journal = Global Public Health | volume = 8 | issue = 10 | pages = 1138–1150 | year = 2013 | pmid = 24294986 | pmc = 4098042 | doi = 10.1080/17441692.2013.859720 }}</ref><ref name=Njeru >{{cite journal | vauthors = Njeru I, Ajack Y, Muitherero C, Onyango D, Musyoka J, Onuekusi I, Kioko J, Muraguri N, Davis R | title = Did the call for boycott by the Catholic bishops affect the polio vaccination coverage in Kenya in 2015? A cross-sectional study | journal = The Pan African Medical Journal | volume = 24 | pages = 120 | year = 2016 | pmid = 27642458 | pmc = 5012825 | doi = 10.11604/pamj.2016.24.120.8986 }}</ref> In Afghanistan and Pakistan, fears that the vaccine contained contraceptives were one reason given by the Taliban in issuing ''fatwas'' against polio vaccination.<ref name=Njeru /><ref name="Religious opposition" /><ref>{{cite news | vauthors = Walsh D |location=Peshawar |url=https://www.theguardian.com/world/2007/feb/15/pakistan.topstories3 |title=Polio cases jump in Pakistan as clerics declare vaccination an American plot |work=The Guardian |date=14 February 2007 |access-date=29 March 2014 |archive-date=29 March 2014 |archive-url=https://web.archive.org/web/20140329160002/http://www.theguardian.com/world/2007/feb/15/pakistan.topstories3 |url-status=live }}</ref> Religious boycotts based on contamination concerns have not been limited to the Muslim world. In 2015, after claiming that a tetanus vaccine contained a contraceptive, a group of Kenyan Catholic bishops called on their followers to boycott a planned round of polio vaccination. This did not have a major effect on vaccination rates, and dialog along with vaccine testing forestalled further boycott calls.<ref name=Njeru />
Other religion-inspired refusals arise from concern over whether the virus contains pig-derived products, and hence are ''haram'' (forbidden) in Islam,<ref>{{cite journal | vauthors = Ahmed A, Lee KS, Bukhsh A, Al-Worafi YM, Sarker MM, Ming LC, Khan TM | title = Outbreak of vaccine-preventable diseases in Muslim majority countries | journal = Journal of Infection and Public Health | volume = 11 | issue = 2 | pages = 153–155 | year = 2018 | pmid = 28988775 | doi = 10.1016/j.jiph.2017.09.007 | doi-access = free }}</ref> concern that vaccine production may have involved a prohibited taking of animal life,<ref name=Njeru /> or a resistance to interfering with disease processes perceived to be divinely-directed.<ref name=Ghani /><ref name=Njeru /> Concerns were addressed through extensive outreach, directed both toward the communities involved and respected clerical bodies, as well as promoting local ownership of the eradication campaign in each region. In early 2012, some parents refused to get their children vaccinated in Khyber Pakhtunkhwa (KPK) and in the Federally Administered Tribal Areas (FATA) but religious refusals in the rest of the country had "decreased manifold".<ref name="WHO rejects rumours">{{cite news|title=WHO rejects polio rumours|url=https://www.dawn.com/news/698270/who-rejects-polio-rumours|access-date=3 June 2012|newspaper=Dawn|date=26 February 2012| vauthors = Teepu IA |archive-date=29 May 2012|archive-url=https://web.archive.org/web/20120529160851/http://dawn.com/2012/02/26/who-rejects-polio-rumours/|url-status=live}}</ref> Even with the express support of political leaders, polio workers or their accompanying security guards have been kidnapped, beaten, or assassinated.<ref name="Religious opposition">{{cite journal | vauthors = Warraich HJ | title = Religious opposition to polio vaccination | journal = Emerging Infectious Diseases | volume = 15 | issue = 6 | pages = 978a–978 | date = June 2009 | pmid = 19523311 | pmc = 2727330 | doi = 10.3201/eid1506.090087 }}</ref>
Skepticism in the Muslim world was exacerbated when it was learned that in 2011 the Central Intelligence Agency (CIA) had conducted a fake hepatitis B immunization campaign, hoping to collect blood samples from Osama bin Laden's compound in Abbottabad in order to confirm the genetic identity of the children living there, and by implication his own presence, leading directly to his killing.<ref name="Heidi Larson">{{cite news|title=The CIA's fake vaccination drive has damaged the battle against polio|url=https://www.theguardian.com/commentisfree/2012/may/27/cia-fake-vaccination-polio|access-date=3 June 2012|newspaper=The Guardian|date=27 May 2012| vauthors = Larson H |archive-date=11 July 2020|archive-url=https://web.archive.org/web/20200711223941/https://www.theguardian.com/commentisfree/2012/may/27/cia-fake-vaccination-polio|url-status=live}}</ref><ref name="BBC20111006">{{cite news|url=https://www.bbc.co.uk/news/world-south-asia-15206639|title=Bin Laden death: 'CIA doctor' accused of treason|publisher=BBC News Online|date=6 October 2011|access-date=8 October 2011|archive-date=11 July 2020|archive-url=https://web.archive.org/web/20200711205253/https://www.bbc.co.uk/news/world-south-asia-15206639|url-status=live}}</ref> In a letter written to CIA director Leon Panetta, the InterAction Alliance, a union of about 200 U.S.-based non-government organizations, deplored the actions of the CIA in using a vaccination campaign as a cover.<ref name="Dawn: NGO assail CIA">{{cite news| vauthors = Teepu IA |title=American NGOs assail CIA over fake polio drive|url=https://www.dawn.com/news/699586/american-ngos-assail-cia-over-fake-polio-drive|access-date=27 May 2012|newspaper=Dawn|date=2 March 2012|archive-date=1 November 2013|archive-url=https://web.archive.org/web/20131101035703/http://dawn.com/news/699586/american-ngos-assail-cia-over-fake-polio-drive|url-status=live}}</ref> Pakistan reported the world's highest number of polio cases (198),<ref name="WHO rejects rumours"/><ref name="Orla Guerin">{{cite news|title='Emergency plan' to eradicate polio launched|url=https://www.bbc.co.uk/news/health-18186393|access-date=27 May 2012|newspaper=BBC News Online|date=24 May 2012| vauthors = Guerin O |archive-date=26 May 2012|archive-url=https://web.archive.org/web/20120526234806/http://www.bbc.co.uk/news/health-18186393|url-status=live}}</ref> in 2011.<ref name="Saeed Shah">{{cite news|title=CIA tactics to trap Bin Laden linked with polio crisis, say aid groups|url=https://www.theguardian.com/world/2012/mar/02/aid-groups-cia-osama-bin-laden-polio-crisis|access-date=27 May 2012|newspaper=The Guardian|date=2 March 2012| vauthors = Shah A |archive-date=11 September 2013|archive-url=https://web.archive.org/web/20130911005757/http://www.theguardian.com/world/2012/mar/02/aid-groups-cia-osama-bin-laden-polio-crisis|url-status=live}}</ref> and more than 60 polio vaccination workers were killed between December 2012 and April 2014. In May 2014, CIA director John Brennan prohibited his agency both from using vaccinations to cover operations and from testing samples collected by authentic vaccination campaigns.<ref>{{cite news |title=White House: CIA has ended use of vaccine programmes |work=BBC News |date=19 May 2014 |access-date=15 June 2022 |url=https://www.bbc.com/news/world-us-canada-27489045}}</ref>
Polio vaccination efforts have also faced resistance in another form. The priority placed on vaccination by national authorities has turned it into a bargaining chip, with communities and interest groups resisting vaccination, not due to direct opposition, but to leverage other concessions from governmental authorities. In Nigeria this has taken the form of 'block rejection' of vaccination that is only resolved when state officials agree to repair or improve schools and health-care facilities, pave roads or install electricity.<ref>{{cite news |title=Polio is back in Nigeria, and the next vaccination campaign may have a surprising consequence | vauthors = Grossman S, Phillips J, Rosenzweig L |url=https://www.washingtonpost.com/news/monkey-cage/wp/2016/08/23/polio-is-back-in-nigeria-heres-why-local-communities-will-bargain-hard-on-the-next-vaccination-surge/ |newspaper=The Washington Post |date=23 August 2016 |access-date=23 August 2016 |archive-date=24 August 2016 |archive-url=https://web.archive.org/web/20160824020755/https://www.washingtonpost.com/news/monkey-cage/wp/2016/08/23/polio-is-back-in-nigeria-heres-why-local-communities-will-bargain-hard-on-the-next-vaccination-surge/ |url-status=live }}</ref> There have been several instances of threatened boycotts by health workers in Pakistan over payment disputes.<ref>{{cite news|title=Protesting health workers threaten to boycott anti-polio drive|url=https://www.dawn.com/news/1205076|newspaper=Dawn|date=5 September 2015|access-date=23 August 2016|archive-date=27 August 2016|archive-url=https://web.archive.org/web/20160827125249/http://www.dawn.com/news/1205076|url-status=live}}</ref><ref>{{cite news|title=Up in arms: EPI workers threaten to boycott polio drives in FATA|url=https://tribune.com.pk/story/1091625/up-in-arms-epi-workers-threaten-to-boycott-polio-drives-in-fata|newspaper=The Express Tribune|date=26 April 2016|access-date=23 August 2016|archive-date=25 August 2016|archive-url=https://web.archive.org/web/20160825192727/http://tribune.com.pk/story/1091625/up-in-arms-epi-workers-threaten-to-boycott-polio-drives-in-fata/|url-status=live}}</ref> Some governments have been accused of withholding vaccination or the necessary accompanying infrastructure from regions where opposition to their rule is high.<ref>{{cite magazine| vauthors = Sparrow A |title=Syria's Polio Epidemic: The Suppressed Truth|magazine=The New York Review of Books|date=20 February 2014|access-date=31 August 2018|url=https://www.nybooks.com/articles/2014/02/20/syrias-polio-epidemic-suppressed-truth/|archive-date=1 September 2018|archive-url=https://web.archive.org/web/20180901044511/https://www.nybooks.com/articles/2014/02/20/syrias-polio-epidemic-suppressed-truth/|url-status=live}}</ref>
== Polio eradication criteria == A country is regarded as polio-free or non-endemic if no cases have been detected for a year.<ref name="WHO_Nigeria">{{Cite press release|url=https://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/|title=WHO Removes Nigeria from Polio-Endemic List|website=World Health Organization (WHO)|access-date=10 October 2017|archive-date=27 September 2015|archive-url=https://web.archive.org/web/20150927225439/http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/}}</ref><ref name="WHO_Laos" /> However, it is still possible for polio to circulate under these circumstances, as was the case for Nigeria, where a particular strain of virus resurfaced after five years in 2016.<ref name="WHO_2018" /> This can be due to chance, limited surveillance and under-vaccinated populations.<ref name="McCarthy_2016">{{cite journal | vauthors = McCarthy KA, Chabot-Couture G, Shuaib F | title = A spatial model of Wild Poliovirus Type 1 in Kano State, Nigeria: calibration and assessment of elimination probability | journal = BMC Infectious Diseases | volume = 16 | issue = 1 | article-number = 521 | date = September 2016 | pmid = 27681708 | pmc = 5041410 | doi = 10.1186/s12879-016-1817-3 | doi-access = free }}</ref> Moreover, for WPV1—the only type of the virus which is currently circulating following the eradication of WPV2 and WPV3—only 1 in 200 infection cases exhibit symptoms of polio paralysis in non-vaccinated children.<ref name="Kalkowska 66">{{cite journal | vauthors = Kalkowska DA, Duintjer Tebbens RJ, Pallansch MA, Cochi SL, Wassilak SG, Thompson KM | title = Modeling undetected live poliovirus circulation after apparent interruption of transmission: implications for surveillance and vaccination | journal = BMC Infectious Diseases | volume = 15 | article-number = 66 | date = February 2015 | pmid = 25886823 | pmc = 4344758 | doi = 10.1186/s12879-015-0791-5 | doi-access = free }}</ref> Therefore, even a single case is indicative of an epidemic.<ref name="LatAmCarib">{{Cite web | veditors = Kinder M | url=https://www.cgdev.org/doc/millions/MS_case_5.pdf | title=Case 5: Eliminating Polio in Latin America and the Caribbean | website=Center for Global Development (CGD) | access-date=10 October 2017 | archive-date=9 June 2017 | archive-url=https://web.archive.org/web/20170609222307/https://www.cgdev.org/doc/millions/MS_case_5.pdf | url-status=live | quote=... for each case ..., the community is further threatened by another 2,000 to 3,000 contagious carriers ... rendering even a single documented case indicative of an epidemic }}</ref>
Certification of wild poliovirus eradication requires three consecutive years without case reports, in the presence of reliable disease surveillance networks.<ref>{{cite web |title=Polio containment and certification |url=https://www.emro.who.int/polio-eradication/about-eradication/polio-containment-and-certification.html |website=World Health Organization - Regional Office for the Eastern Mediterranean |language=en-gb}}</ref><ref>{{cite web |title=GPEI-Certification |url=https://polioeradication.org/polio-today/preparing-for-a-polio-free-world/certification/ |access-date=9 July 2023 |archive-date=17 February 2017 |archive-url=https://web.archive.org/web/20170217164339/https://polioeradication.org/polio-today/preparing-for-a-polio-free-world/certification/ |url-status=dead }}</ref> Wild poliovirus type{{nbsp}}2 was certified eradicated in 2015, the last case having been detected in 1999.<ref name="News stories" /> Wild poliovirus type{{nbsp}}3 has not been detected since 2012, and was certified eradicated in 2019.<ref name="WPV3gone">{{Cite web|url=http://polioeradication.org/news-post/two-out-of-three-wild-poliovirus-strains-eradicated/|title=Two out of three wild poliovirus strains eradicated|access-date=24 October 2019|publisher=Global Polio Eradication Initiative (GPEI)|archive-date=24 October 2019|archive-url=https://web.archive.org/web/20191024163941/http://polioeradication.org/news-post/two-out-of-three-wild-poliovirus-strains-eradicated/}}</ref>
== Post-eradication plans == Beginning at certification of complete WPV eradication, the post-certification strategy will come into effect,<ref name="PCS">{{cite book |url=https://polioeradication.org/wp-content/uploads/2018/04/polio-post-certification-strategy-20180424-2.pdf |title=Polio Post-Certification Strategy |publisher=Global Polio Eradication Initiative |archive-date=14 June 2018 |access-date=9 July 2023 |archive-url=https://web.archive.org/web/20180614084828/http://polioeradication.org/wp-content/uploads/2018/04/polio-post-certification-strategy-20180424-2.pdf |url-status=dead }}</ref>{{rp|6}} with program priorities shifting towards outbreak preparedness and containment of existing virus material rather than circulating disease.<ref name="PES2022">{{cite web |title=GPEI Strategy 2022-2026 |url=https://polioeradication.org/wp-content/uploads/2022/06/Polio-Eradication-Strategy-2022-2026-Delivering-on-a-Promise.pdf |publisher=Global Polio Eradication Initiative}}</ref>{{rp|40}} Vaccination for WPV1 will cease one year following eradication certification, and eradication of vaccine-derived poliovirus is then targeted for 2030.<ref name="PES2022" />{{rp|21}}
Where possible, the number of facilities conducting operations with poliovirus is to be reduced significantly; and the use of wild poliovirus is to be abandoned altogether in favour of genetically stabilized attenuated strains where possible.<ref>{{cite web |date=6 May 2022 |title=Poliomyelitis eradication — Report by the Director-General |url=https://apps.who.int/gb/ebwha/pdf_files/WHA75/A75_23-en.pdf |access-date=2024-01-09 |publisher=Seventy-Fifth World Health Assembly |page=5}}</ref> {{As of|2021|05|post=,}} there are 74 designated Poliovirus Essential Facilities (PEFs) across 24 countries<ref name="GAP4">{{cite book |url=https://polioeradication.org/wp-content/uploads/2022/07/WHO-Global-Action-Plan-for-Poliovirus-Containment-GAPIV.pdf |title=WHO Global Action Plan for Poliovirus Containment |publisher=Global Polio Eradication Initiative}}</ref>{{rp|41}} where work on poliovirus can be carried out. These facilities are currently involved in producing materials to assist the eradication initiative, and perform crucial research which may prevent future outbreaks. After certification, these facilities retain the equipment and materials to continue vaccine production in the event of deliberate or accidental release.<ref name="GAP4" />{{rp|17}} Work on Poliovirus outside of the PEFs will be prohibited, and stocks in laboratories that are not designated as PEFs must either be transferred to a PEF or destroyed.<ref name="GAP4" />{{rp|26}}{{Clear}}
== Timeline == {| class="wikitable floatright" style="font-size:85%" |+ International wild poliovirus cases by year |- ! Year !! Estimated !! Recorded |- | '''1975''' || — || 49,293<ref name="Watch" /> |- | colspan=3 align="center"| ... |- | '''1980''' || 400,000<ref name="Lee_1995">{{cite web|url=http://www.unicef.org/pon95/heal0002.html|title=Ending polio—now or never?| vauthors = Lee JW |year=1995|work=The Progress of Nations|publisher=Unicef|access-date=2 February 2007 |archive-url=https://web.archive.org/web/20180105233539/https://www.unicef.org/pon95/heal0002.html |archive-date=5 January 2018 }}</ref> || 52,552<ref name="Watch" /> |- | colspan=3 align="center"| ... |- | '''1985''' || — || 38,637<ref name="Watch" /> |- | colspan=3 align="center"| ... |- | 1988 || 350,000<ref name="Aylward_2005">{{cite journal | vauthors = Aylward RB, Linkins J | title = Polio eradication: mobilizing and managing the human resources | journal = Bulletin of the World Health Organization | volume = 83 | issue = 4 | pages = 268–273 | date = April 2005 | pmid = 15868017 | pmc = 2626205 | url = https://www.who.int/bulletin/volumes/83/4/268.pdf }}</ref> || 35,251<ref name="Watch" /> |- | colspan=3 align="center"| ... |- | '''1990''' || — || 23,484<ref name="Watch" /> |- | colspan=3 align="center"| ... |- | 1993 || 100,000<ref name="Lee_1995" /> || 10,487<ref name="Watch" /> |- | colspan=3 align="center"| ... |- | '''1995''' || — || 7,035<ref name="Watch" /> |- | colspan=3 align="center"| ... |- | '''2000''' || — || 719<ref name="WHO_2015">{{cite web|url=https://extranet.who.int/polis/public/CaseCount.aspx|title=AFP/Polio Case Count|date=6 January 2015|publisher=World Health Organization (WHO)|access-date=10 January 2015|archive-date=2 April 2015|archive-url=https://web.archive.org/web/20150402165939/https://extranet.who.int/polis/public/CaseCount.aspx|url-status=live}}</ref> |- | colspan=3 align="center"| ... |- | '''2005''' || — || 1,979<ref name="WHO_2015" /> |- | colspan=3 align="center"| ... |- | '''2010''' || — || 1,352<ref name="WHO_2015" /> |- | 2011 || — || 650<ref name="WHO_2015" /> |- | 2012 || — || 223<ref name="WHO_2015" /> |- | 2013 || — || 416<ref name="WHO_2015" /> |- | 2014 || — || 359<ref name="WHO_2015" /> |- | '''2015''' || — || 74<ref name="WHO_2015" /> |- |2016 |— |37<ref name="WHO_2015" /> |- |2017 |— |22<ref name="GWP-Dec2022" /> |- |2018 |— |33<ref name="GWP-Dec2022" /> |- |2019 |— |176<ref name="GWP-Dec2022" /> |- |'''2020''' |— |140<ref name="GWP-Dec2022">{{cite web |date=2022-12-27 |title=Global Wild Poliovirus 2016 - 2022 |url= https://polioeradication.org/wp-content/uploads/2022/12/weekly-polio-analyses-WPV-20221227.pdf |access-date=2023-01-08 |url-status=live |archive-url= https://web.archive.org/web/20221231233514/https://polioeradication.org/wp-content/uploads/2022/12/weekly-polio-analyses-WPV-20221227.pdf |archive-date=2022-12-31 |website=GPEI}}</ref> |- |2021 |— |6<ref name="WPVcurrent" /> |- |2022 |— |30<ref name="WPVcurrent" /> |- |2023 |— |12<ref name="WPVcurrent" /> |- |2024 |— |99<ref name="WPVcurrent" /> |- |'''2025''' |— |51<ref name="WPVcurrent" /> |}
=== 1950s–1987 === [[File:Bundesarchiv Bild 183-71807-0001, Kindergarten, Schutzimpfung gegen Kinderlähmung.jpg|thumb|left|upright|Kindergarten children receive a very early oral polio vaccine in 1960 in East Germany.]] Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries.<ref name="PinkBook">{{cite book |url=https://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf |title=Epidemiology and Prevention of Vaccine-Preventable Diseases |vauthors=((Centers for Disease Control and Prevention)) |publisher=Public Health Foundation |year=2015 |isbn=978-0-9904491-1-9 |veditors=Hamborsky J, Kroger A, Wolfe S |edition=13th |location=Washington, D.C. |access-date=8 September 2017 |archive-url=https://web.archive.org/web/20190630034611/https://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf |archive-date=30 June 2019 |url-status=live}}</ref> Czechoslovakia became the first country in the world to scientifically demonstrate nationwide eradication of poliomyelitis in 1960.<ref>{{cite journal | vauthors = Slonim D | title = [Global eradication of poliomyelitis. On the 80th anniversary of the founding of the National Institute of Health] | language = cs | journal = Epidemiologie, Mikrobiologie, Imunologie | volume = 54 | issue = 3 | pages = 99–108 | date = August 2005 | pmid = 16173520 | url = http://kramerius.medvik.cz/search/pdf/web/viewer.html?pid=uuid:38873207-69b8-11e3-93fe-d485646517a0#page=7 | access-date = 27 August 2020 | url-status = live | format = PDF | trans-title = Global eradication of poliomyelitis. On the 80th anniversary of the founding of the National Institute of Health | archive-url = https://web.archive.org/web/20200827161416/http://kramerius.medvik.cz/search/pdf/web/viewer.html?pid=uuid%3A38873207-69b8-11e3-93fe-d485646517a0#page=7 | archive-date = 27 August 2020 }}</ref> In 1962—just one year after Sabin's oral polio vaccine (OPV) was licensed in most industrialized countries—Cuba began using the oral vaccine in a series of nationwide polio campaigns. The early success of these mass vaccination campaigns suggested that polioviruses could be globally eradicated.<ref name= Hinman>{{cite journal | vauthors = Hinman AR | title = Landmark perspective: Mass vaccination against polio | journal = JAMA | volume = 251 | issue = 22 | pages = 2994–2996 | date = June 1984 | pmid = 6371280 | doi = 10.1001/jama.1984.03340460072029 }}</ref> The Pan American Health Organization (PAHO), under the leadership of Ciro de Quadros, launched an initiative to eradicate polio from the Americas in 1985.<ref name= Fujimura>{{cite web | vauthors = Fujimura SF | title = The Man Who Made Polio History | publisher = Pan American Health Organization | year = 2005 | url = http://www.paho.org/English/DD/PIN/Number22_article2.htm | access-date = 2 February 2007 | archive-date = 11 December 2006 | archive-url = https://web.archive.org/web/20061211202908/http://www.paho.org/English/DD/PIN/Number22_article2.htm | url-status = live }}</ref>
Much of the work towards eradication was documented by Brazilian photographer Sebastião Salgado, as a UNICEF Goodwill Ambassador, in the book ''The End of Polio: Global Effort to End a Disease''.<ref>{{cite press release | title = The End of Polio: Photographs of Sebastião Salgado Opens to Public | url = https://www.cdc.gov/media/pressrel/2007/r070824.htm | date = 24 August 2007 | access-date = 2 June 2008 | publisher = Centers for Disease Control and Prevention (CDC) | archive-date = 29 June 2017 | archive-url = https://web.archive.org/web/20170629081043/https://www.cdc.gov/media/pressrel/2007/r070824.htm | url-status = live }}</ref>
=== 1988–2000 ===
In 1988, the World Health Organization (WHO), together with Rotary International, UNICEF, and the U.S. Centers for Disease Control and Prevention (CDC) passed the Global Polio Eradication Initiative (GPEI), with the goal of eradicating polio by the year 2000. The initiative was inspired by Rotary International's 1985 pledge to raise $120{{nbsp}}million toward immunising all of the world's children against the disease.<ref name= Fujimura/> The last case of wild poliovirus poliomyelitis in the Americas was reported in Peru, August 1991.<ref name= Fujimura/>
On 20 August 1994, the Americas were certified as polio-free.<ref name=MMWR_1994>{{cite journal | title = Certification of poliomyelitis eradication—the Americas, 1994 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 43 | issue = 39 | pages = 720–722 | date = October 1994 | pmid = 7522302 | url = https://www.cdc.gov/mmwr/PDF/wk/mm4339.pdf | access-date = 27 October 2019 | url-status = live | archive-url = https://web.archive.org/web/20170913111612/https://www.cdc.gov/mmwr/PDF/wk/mm4339.pdf | archive-date = 13 September 2017 | author1 = Centers for Disease Control and Prevention (CDC) }}</ref> This achievement was a milestone in efforts to eradicate the disease.
In 1994, the Indian Government launched the Pulse Polio Campaign to eliminate polio. The campaign involves annual vaccination of all children ages 0–5.<ref>{{cite web | title = Pulse Polio Programme | publisher = Government of India; Department of Family Welfare | year = 2013 | url = https://www.chaloafrica.com/wp-content/uploads/2014/06/pulse-polio-programme.pdf | access-date = 10 July 2014 | archive-date = 14 July 2014 | archive-url = https://web.archive.org/web/20140714184702/http://www.chaloafrica.com/wp-content/uploads/2014/06/pulse-polio-programme.pdf | url-status = live }}</ref>
In 1995, Operation MECACAR (Mediterranean, Caucasus, Central Asian Republics, and Russia) was launched; National Immunization Days were coordinated in 19 European and Mediterranean countries.<ref>{{cite web| title = Operation MECACAR |publisher = World Health Organization (WHO) | date = 2 June 2006 | url = http://www.euro.who.int/vaccine/20030724_13 | access-date = 2 February 2007 |archive-url = https://web.archive.org/web/20070729061315/http://www.euro.who.int/vaccine/20030724_13 <!-- Bot retrieved archive --> |archive-date = 29 July 2007}}</ref> In 1998, Melik Minas of Turkey became the last case of polio reported in Europe.<ref>{{cite press release |title=WHO European Region celebrates three polio-free years: certification within reach in 2002 |publisher=World Health Organization (WHO)|url=http://www.euro.who.int/mediacentre/PR/2001/20011217_3 |date=30 November 2001 |access-date=31 July 2007 |archive-url=https://web.archive.org/web/20050922102347/http://www.euro.who.int/mediacentre/pr/2001/20011217_3 |archive-date=22 September 2005 }}</ref> In 1997, Mum Chanty of Cambodia became the last person to contract polio in the Indo-West Pacific region.<ref name=Pacific>{{cite journal | vauthors = Yamazaki S, Toraya H | title = (General News) Major Milestone reached in Global Polio Eradication: Western Pacific Region is certified Polio-Free | journal = Health Education Research | year = 2001 | volume = 16 | pages = 110–111 | issue = 1 | doi = 10.1093/her/16.1.109 |doi-access= | bibcode = 2001PDiff..16..110Y}}</ref> In 2000, the Western Pacific Region (including China) was certified polio-free.<ref name=Pacific />
In October 1999, the last isolation of type{{nbsp}}2 poliovirus occurred in India. This type of poliovirus was subsequently declared eradicated.<ref name= PinkBook/><ref name="News stories">{{Cite web|title = Global Eradication Of Wild Poliovirus Type 2 Declared|url = http://polioeradication.org/news-post/global-eradication-of-wild-poliovirus-type-2-declared/|website = Global Polio Eradication Initiative (GPEI)|access-date = 27 September 2015|archive-date = 12 September 2016|archive-url = https://web.archive.org/web/20160912035013/http://www.polioeradication.org/mediaroom/newsstories/Global-eradication-of-wild-poliovirus-type-2-declared/tabid/526/news/1289/Default.aspx|url-status = live}}</ref>
Also in October 1999, the CORE Group—with funding from the United States Agency for International Development (USAID)—launched its effort to support national eradication efforts at the grassroots level. The CORE Group commenced this initiative in Bangladesh, India, and Nepal in South Asia, and in Angola, Ethiopia, and Uganda in Africa.<ref>{{cite web|title=CORE Group Polio Eradication Initiative |url=http://www.coregroup.org/initiatives/polio.cfm |access-date=10 March 2009 |archive-url=https://web.archive.org/web/20090227134640/http://www.coregroup.org/initiatives/polio.cfm |archive-date=27 February 2009 }}</ref>
=== 2001–2005 === [[File:Poliomyelitis world map - DALY - WHO2004.svg|thumb|Disability-adjusted life year for poliomyelitis per 100,000 inhabitants in 2004 {{Col-begin}} {{Col-break}} {{legend|#b3b3b3|no data}} {{legend|#ffff65|<0.3}} {{legend|#fff200|0.3–0.75}} {{legend|#ffdc00|0.75–1.2}} {{legend|#ffc600|1.2–1.65}} {{legend|#ffb000|1.65–2.1}} {{legend|#ff9a00|2.1–2.55}} {{Col-break}} {{legend|#ff8400|2.55–3}} {{legend|#ff6e00|3–4}} {{legend|#ff5800|4–5}} {{legend|#ff4200|5–7.5}} {{legend|#ff2c00|7.5–10}} {{legend|#cb0000|>10}} {{col-end}}]]
By 2001, 575{{nbsp}}million children (almost one-tenth the world's population) had received some two billion doses of oral polio vaccine.<ref name=Rotary.Timeline>{{cite web|title=PolioPlus Timeline |publisher=Rotary International |url=http://www.rotary.org/en/serviceandfellowship/polio/timeline/Pages/ridefault.aspx |access-date=11 March 2011 |archive-url=https://web.archive.org/web/20110220222008/http://www.rotary.org/en/ServiceAndFellowship/Polio/Timeline/Pages/ridefault.aspx |archive-date=20 February 2011 }}</ref> The World Health Organization announced that Europe was polio-free on 21 June 2002, in the Copenhagen Glyptotek.<ref>{{cite press release | title = Europe achieves historic milestone as Region is declared polio-free | publisher = World Health Organization (WHO) | date = 21 June 2002 | url = http://www.euro.who.int/mediacentre/PR/2002/20020620_1 | archive-url=https://web.archive.org/web/20100516220858/http://www.euro.who.int/mediacentre/PR/2002/20020620_1 | archive-date=16 May 2010 | access-date = 2 February 2007 }}</ref>
In 2002, an outbreak of polio occurred in India. The number of planned polio vaccination campaigns had recently been reduced, and populations in northern India, particularly from the Islamic background, engaged in mass resistance to immunization.<ref name=":0">{{Cite web |date=June 2013 |title=Eradicating Polio: Working with religious leaders to enhance community ownership |url=https://iple.unicef.in/files/ckuploads/files/Polio%20eradication%20in%20UP%20-%20Religious%20Leaders.pdf |access-date=2025-03-27 |publisher=UNICEF |pages=7–9, 22 |language=en}}</ref> At this time, the Indian state of Uttar Pradesh accounted for nearly two thirds of total worldwide cases reported.<ref>{{cite press release | title = WHO Director-General calls India 'number 1' polio eradication priority | work = World Health Organization (WHO) | url =https://www.who.int/mediacentre/news/releases/2003/pr30/en/index.html | date = 7 April 2003 | access-date = 31 July 2007 | archive-date = 19 June 2007 | archive-url = https://web.archive.org/web/20070619143940/http://www.who.int/mediacentre/news/releases/2003/pr30/en/index.html }}</ref> (See the 2002 global polio incidence map.) However, by 2004, India had adopted strategies to increase ownership of polio vaccinations in marginalized populations, and the immunity gap in vulnerable groups rapidly closed.<ref name=":0" />
In August 2003, rumors spread in some states in Nigeria, especially Kano, that the vaccine caused sterility in girls. This resulted in the suspension of immunization efforts in the state, causing a dramatic rise in polio rates in the already endemic country.<ref name="Jegede2007">{{cite journal | vauthors = Jegede AS | title = What led to the Nigerian boycott of the polio vaccination campaign? | journal = PLOS Medicine | volume = 4 | issue = 3 | pages = e73 | date = March 2007 | pmid = 17388657 | pmc = 1831725 | doi = 10.1371/journal.pmed.0040073 | doi-access = free }}</ref> On 30 June 2004, the WHO announced that after a 10-month ban on polio vaccinations, Kano had pledged to restart the campaign in early July. During the ban the virus spread across Nigeria and into 12 neighboring countries that had previously been polio-free.<ref name=Fujimura/> By 2006, this ban would be blamed for 1,500 children being paralyzed,<ref>{{Cite journal |last=Jegede |first=Ayodele Samuel |date=March 2007 |title=What led to the Nigerian boycott of the polio vaccination campaign? |journal=PLOS Medicine |volume=4 |issue=3 |page=e73 |doi=10.1371/journal.pmed.0040073 |doi-access=free |issn=1549-1676 |pmc=1831725 |pmid=17388657}}</ref> and had cost $450{{nbsp}}million for emergency activities.<ref>{{Cite web |date=2006-10-15 |title=Polio epidemic lurks in four nations |url=https://www.washingtontimes.com/news/2006/oct/15/20061015-112127-6493r/ |access-date=2025-03-27 |website=The Washington Times |language=en-US}}</ref> In addition to the rumors of sterility and the ban by Nigeria's Kano state, civil war and internal strife in Sudan and Côte d'Ivoire have complicated WHO's polio eradication goal. In 2004, 63% of all the polio cases in the world occurred in Nigeria (792 out of 1,265 total).<ref>{{Cite journal |date=May 2005 |title=2004 Annual Report |url=https://iris.who.int/bitstream/handle/10665/69055/WHO_POLIO_05.03.pdf |url-status=dead |journal=Global Polio Eradication Initiative |language=en |publisher=World Health Organization |page=10 |archive-url=https://web.archive.org/web/20240525074846/https://iris.who.int/bitstream/handle/10665/69055/WHO_POLIO_05.03.pdf |archive-date=2024-05-25}}</ref><ref>{{Cite web |date=2005-04-19 |title=Nigeria records drop in new polio cases |url=https://www.nbcnews.com/id/wbna7558592 |access-date=2025-03-27 |website=NBC News |language=en}}</ref> thumb|right|Countries with polio cases in 2005 {{legend|red|Polio was endemic}} {{legend|orange|Polio had re-established transmission}} {{legend|green|Cases were importation-related}} {{legend|blue|All cases were due to circulating vaccine-derived virus}}
In May 2004, the first case of the polio outbreak in Sudan was detected. The reemergence of polio led to stepped up vaccination campaigns. In the city of Darfur, 78,654 children were immunized and 20,432 more in southern Sudan (Yirol and Chelkou).<ref>{{cite news|url=http://www.noticias.info/Archivo/2005/200505/20050511/20050511_65088.shtm|archive-url=https://web.archive.org/web/20060812160409/http://www.noticias.info/Archivo/2005/200505/20050511/20050511_65088.shtm|archive-date=12 August 2006|title=Sudan: Bulletin No. 28|date=11 May 2005|work=International Committee of the Red Cross (ICRC)|access-date=7 February 2007|url-status=live}}</ref>
In 2005, there were 1,979 cases of wild poliovirus (excluding vaccine-derived poliovirus).<ref name="GPEI_2012">{{Cite web|url = http://www.polioeradication.org/Portals/0/Document/Data&Monitoring/Wild_poliovirus_list_2005_2011_03Jan.pdf|title = Wild Poliovirus List 2005-2011|date = 3 January 2012|access-date = 13 September 2015|website = Global Polio Eradication Initiative (GPEI)|archive-url = https://web.archive.org/web/20160304192124/http://www.polioeradication.org/Portals/0/Document/Data%26Monitoring/Wild_poliovirus_list_2005_2011_03Jan.pdf|archive-date = 4 March 2016}}</ref> Most cases were located in two areas: the Indian subcontinent and Nigeria. Eradication efforts in the Indian sub-continent met with a large measure of success. Using the Pulse Polio campaign to increase polio immunization rates, India recorded just 66 cases in 2005, down from 135 cases reported in 2004, 225 in 2003, and 1,600 in 2002.<ref name=WHO.2014>{{cite web| title = WHO Vaccine Preventable Diseases: Monitoring system |publisher = World Health Organization (WHO) | year = 2014 | url =https://www.who.int/entity/immunization_monitoring/data/incidence_series.xls |archive-url=https://web.archive.org/web/20070511120051/http://www.who.int/immunization_monitoring/data/incidence_series.xls |archive-date=11 May 2007 | access-date = 21 October 2014|format=XLS}}</ref>
Yemen, Indonesia, and Sudan, countries that had been declared polio-free since before 2000, each reported hundreds of cases—probably imported from Nigeria.<ref name=Nigeria>{{cite news | vauthors = Balint-Kurti D | title = Polio Spreads From Nigeria After Claims | agency = Associated Press | date = 4 May 2005 | url = https://www.ar15.com/forums/general/-/5-348684/?page=1 | access-date = 19 January 2013 | archive-date = 5 November 2018 | archive-url = https://web.archive.org/web/20181105224635/https://www.ar15.com/forums/general/-/5-348684/?page=1 | url-status = live }}</ref> On 5 May 2005, news reports broke that a new case of polio was diagnosed in Java, Indonesia, and the virus strain was suspected to be the same as the one that has caused outbreaks in Nigeria. New public fears over vaccine safety, which were unfounded, impeded vaccination efforts in Indonesia. In summer 2005, the WHO, UNICEF and the Indonesian government made new efforts to lay the fears to rest, recruiting celebrities and religious leaders in a publicity campaign to promote vaccination.<ref>{{cite news | vauthors = Aglionby J | title = Indonesia faces polio challenge | work = The Guardian | date = 2 September 2005 | url = https://www.theguardian.com/world/2005/sep/02/indonesia.worlddispatch | access-date = 7 February 2007 | archive-date = 29 August 2013 | archive-url = https://web.archive.org/web/20130829174657/http://www.theguardian.com/world/2005/sep/02/indonesia.worlddispatch | url-status = live }}</ref>
In the United States on 29 September 2005, the Minnesota Department of Health identified the first occurrence of vaccine-derived poliovirus (VDPV) transmission in the United States since OPV was discontinued in 2000. The poliovirus type{{nbsp}}1 infection occurred in an unvaccinated, immunocompromised infant girl aged seven months (the index patient) in an Amish community whose members predominantly were not vaccinated for polio.<ref name="Bahta_2005">{{cite journal | title = Poliovirus infections in four unvaccinated children--Minnesota, August-October 2005 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 54 | issue = 41 | pages = 1053–1055 | date = October 2005 | pmid = 16237378 | url = https://www.cdc.gov/mmwr/pdf/wk/mm54d1014.pdf | access-date = 27 October 2019 | url-status = live | archive-url = https://web.archive.org/web/20200709115850/https://www.cdc.gov/mmwr/pdf/wk/mm54d1014.pdf | archive-date = 9 July 2020 | author1 = Centers for Disease Control and Prevention (CDC) }}</ref>
=== 2006–2010 ===
In 2006, only four countries in the world (Nigeria, India, Pakistan, and Afghanistan) were reported to have endemic polio. Cases in other countries are attributed to importation. A total of 1,997 cases worldwide were reported in 2006; of these the majority (1,869 cases) occurred in countries with endemic polio.<ref name="GPEI_2012" /> Nigeria accounted for the majority of cases (1,122 cases) but India reported more than ten times more cases in 2006 than in 2005 (676 cases, or 30% of worldwide cases). Pakistan and Afghanistan reported 40 and 31 cases respectively in 2006. Polio re-surfaced in Bangladesh after nearly six years of absence with 18 new cases reported. "Our country is not safe, as neighbours India and Pakistan are not polio free", declared Health Minister ASM Matiur Rahman.<ref name="BBC World">{{cite news | title = Bangladesh begins new polio drive | url = https://news.bbc.co.uk/2/hi/south_asia/6412835.stm | work = BBC News | date = 2 March 2007 | access-date = 31 July 2007 | archive-date = 25 April 2019 | archive-url = https://web.archive.org/web/20190425062256/http://news.bbc.co.uk/2/hi/south_asia/6412835.stm | url-status = live }}</ref> (See: Map of reported polio cases in 2006)
In 2007, there were 1,315 cases of poliomyelitis reported worldwide.<ref name="GPEI_2012" /> Over 60% of cases (874) occurred in India. In Nigeria, the number of polio cases fell dramatically, from 1,122 cases reported in 2006 to 285 cases in 2007. Officials credit the drop in new infections to improved political control in the southern states and resumed immunisation in the north, where Muslim clerics led a boycott of vaccination in late 2003. Local governments and clerics allowed vaccinations to resume on the condition that the vaccines be manufactured in Indonesia, a majority Muslim country, and not in the United States.<ref name=Nigeria/> Turai Yar'Adua, wife of recently elected Nigerian president Umaru Yar'Adua, made the eradication of polio one of her priorities. Attending the launch of immunization campaigns in Birnin Kebbi in July 2007, Turai Yar'Adua urged parents to vaccinate their children and stressed the safety of oral polio vaccine.<ref>{{cite web |url=http://www.polioeradication.org/content/general/LatestNews200707.asp |title=First Lady of Nigeria inaugurates vaccination campaigns |access-date=24 January 2008 |date=30 July 2007 |work=Global Polio Eradication Initiative (GPEI) |archive-url = https://web.archive.org/web/20071209001901/http://www.polioeradication.org/content/general/LatestNews200707.asp <!-- Bot retrieved archive --> |archive-date = 9 December 2007}}</ref>
In July 2007, a student traveling from Pakistan imported the first polio case to Australia in over 20 years.<ref>{{cite news | vauthors = Yusufzai A | title = Pakistan polio case in Australia | work = BBC News | date = 30 July 2007 | access-date = 8 August 2007 | url = https://news.bbc.co.uk/2/hi/south_asia/6922991.stm | archive-date = 31 December 2016 | archive-url = https://web.archive.org/web/20161231195825/http://news.bbc.co.uk/2/hi/south_asia/6922991.stm | url-status = live }}</ref> Other countries with significant numbers of wild polio virus cases include the Democratic Republic of the Congo, which reported 41 cases, Chad with 22 cases, and Niger and Myanmar, each of which reported 11 cases.<ref name="GPEI_2012" />
In 2008, 18 countries reported cases and the total number of cases was 1,651. Of these, 1,505 occurred in the four endemic countries and 146 elsewhere. The largest numbers were in Nigeria (798 cases) and India (559 cases): these two countries combined had 82.2 percent of all cases. Outside endemic countries, Chad reported the greatest number (37 cases).<ref name="GPEI_2012" />
In 2009, a total of 1,604 cases were reported across 23 countries. Four endemic countries accounted for 1,256 of these, with the remaining 348 in 19 sub-Saharan countries with imported cases or re-established transmission. Once again, the largest numbers were in India (741) and Nigeria (388).<ref name="GPEI_2012" /> All other countries had less than one hundred cases: Pakistan had 89 cases, Afghanistan 38, Chad 64, Sudan 45, Guinea 42, Angola 29, Côte d'Ivoire 26, Benin 20, Kenya 19, Burkina Faso 15, Niger 15, the Central African Republic 14, Mauritania 13, and Liberia and Sierra Leone both had 11. The following countries had single-digit numbers of cases: Uganda with 8 cases, Togo 6, Cameroon 3, the Democratic Republic of the Congo 3, Burundi 2, and Mali 2.
According to figures updated in April 2012, the WHO reported that there were 1,352 cases of wild polio across 20 countries in 2010. Reported cases of polio were down 95% in Nigeria (to a historic low of 21 cases) and 94% in India (to a historic low of 42 cases) compared to the previous year, with little change in Afghanistan (from 38 to 25 cases) and an increase in cases in Pakistan (from 89 to 144 cases). An acute outbreak in Tajikistan gave rise to 460 cases (34% of the global total), and was associated with a further 18 cases across Central Asia (Kazakhstan and Turkmenistan) and the Russian Federation, with the most recent case from this region being reported from Russia 25 September. These were the first cases in the WHO European region since 2002. The Republic of the Congo (Brazzaville) saw an outbreak with 441 cases (30% of the global total). At least 179 deaths were associated with this outbreak, which is believed to have been an importation from the ongoing type{{nbsp}}1 outbreak in Angola (33 cases in 2010) and the Democratic Republic of the Congo (100 cases).<ref name="GPEI_2012" /><ref name="Wildlist01Jan13">{{cite web|url=http://www.polioeradication.org/Portals/0/Document/Data&Monitoring/Wild_poliovirus_list_2007_2012_1Jan.pdf|title=WHO Wild Poliovirus List|archive-url=https://web.archive.org/web/20130518114944/http://polioeradication.org/Portals/0/Document/Data%26Monitoring/Wild_poliovirus_list_2007_2012_1Jan.pdf|archive-date=18 May 2013|access-date=3 February 2013|publisher=Global Polio Eradication Initiative (GPEI)}}</ref> {{clear}}
=== 2011–2015 === thumb|right|Countries with polio cases in 2011 thumb|left|Polio vaccination in Tehran. In 2011, 650 WPV cases were reported across sixteen countries: the four endemic countries—Pakistan, Afghanistan, Nigeria, and India—as well as twelve others.<ref name="GPEI_2015" /><ref>{{cite journal |title=Evaluating Surveillance Indicators Supporting the Global Polio Eradication Initiative, 2011–2012 |journal=Morbidity and Mortality Weekly Report |date=12 April 2013 |volume=62 |issue=14 |pages=270–274|url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6214a4.htm |access-date=16 August 2024 |publisher=Centers for Disease Control and Prevention|pmid=23575241 |author1=Centers for Disease Control and Prevention (CDC) |pmc=4604901 }}</ref> Polio transmission recurred in Angola, Chad and the Democratic Republic of the Congo.<ref>{{cite journal |title=Progress Toward Global Polio Eradication – Africa, 2011 |journal=Morbidity and Mortality Weekly Report |date=23 March 2012 |volume=61 |issue=11 |pages=190–194 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6111a4.htm |access-date=16 August 2024 |publisher=Centers for Disease Control and Prevention|pmid=22437913 |author1=Centers for Disease Control and Prevention (CDC) }}</ref> Kenya reported its first case since 2009,<ref>{{cite journal |first1=Ahmed |last1=Arale |first2=Mercy |last2=Lutukai |first3=Somane |last3=Mohamed |first4=Lydia |last4=Bologna |first5=Katherine V. |last5=Stamidis |title=Preventing Importation of Poliovirus in the Horn of Africa: The Success of the Cross-Border Health Initiative in Kenya and Somalia |journal=American Journal of Tropical Medicine and Hygiene |date=2019 |volume=101 |issue=Suppl 4 |pages=100–106 |doi=10.4269/ajtmh.19-0040 |pmid=31760979 |url=https://www.ajtmh.org/view/journals/tpmd/101/4_Suppl/article-p100.xml |access-date=16 August 2024|quote=Likewise, in Kenya, two cases in Garissa County were reported in 2006, 19 cases in Turkana County in 2009, and one case in Rongo district in 2011.|pmc=6776092 }}</ref> while China reported 21 cases, mostly among the Uyghurs of Hotan prefecture, Xinjiang, the first non-imported cases since 1994.<ref>{{cite web |title=China – one year polio-free |url=https://polioeradication.org/news/china-one-year-polio-free/ |website=Global Polio Eradication Initiative |access-date=16 August 2024 |date=9 October 2012}}</ref><ref>{{cite journal |first1=Hui-Ming |last1=Luo |first2=Yong |last2=Zhang |first3=Xin-Qi |last3=Wang |first4=Wen-Zhou |last4=Yu |first5=Ning |last5=Wen |first6=Dong-Mei |last6=Yan |first7=Hua-Qing |last7=Wang |first8=Fuerhati |last8=Wushouer |first9=Hai-Bo |last9=Wang |first10=Ai-Qiang |last10=Xu |first11=Jing-Shan |last11=Zheng |first12=De-Xin |last12=Li |first13=Hui |last13=Cui |first14=Jian-Ping |last14=Wang |first15=Shuang-Li |last15=Zhu |first16=Zi-Jian |last16=Feng |first17=Fu-Qiang |last17=Cui |first18=Jing |last18=Ning |first19=Li-Xin |last19=Hao |first20=Chun-Xiang |last20=Fan |first21=Gui-Jun |last21=Ning |first22=Hong-Jie |last22=Yu |first23=Shi-Wen |last23=Wang |first24=Da-Wei |last24=Liu |first25=Dong-Yan |last25=Wang |first26=Jian-Ping |last26=Fu |first27=Ai-Li |last27=Gou |first28=Guo-Min |last28=Zhang |first29=Guo-Hong |last29=Huang |first30=Yuan-Sheng |last30=Chen |first31=Sha-Sha |last31=Mi |first32=Yan-Min |last32=Liu |first33=Da-Peng |last33=Yin |first34=Hui |last34=Zhu |first35=Xin-Chun |last35=Fan |first36=Xin-Lan |last36=Li |first37=Yi-Xin |last37=Ji |first38=Ke-Li |last38=Li |first39=Hai-Shu |last39=Tang |first40=Wen-Bo |last40=Xu |first41=Yu |last41=Wang |first42=Wei-Zhong |last42=Yang |title=Identification and Control of a Poliomyelitis Outbreak in Xinjiang, China |journal=The New England Journal of Medicine |date=21 November 2013 |volume=369 |issue=21 |pages=1981–1990 |doi=10.1056/NEJMoa1303368 |pmid=24256377 |url=https://www.nejm.org/doi/full/10.1056/NEJMoa1303368 |access-date=16 August 2024}}</ref>
The total number of wild-virus cases reported in 2012 was 223, lower than any previous year. These were limited to five countries—Nigeria, Pakistan, Afghanistan, Chad, and Niger—of which all except Nigeria had fewer cases than in 2011.<ref name="GPEI_2015" /> Several additional countries, Chad, the Democratic Republic of the Congo, Somalia, and Yemen, saw outbreaks of circulating vaccine-derived polio. The last reported type{{nbsp}}3 case of polio worldwide had its onset 11 November 2012 in Nigeria; the last wild case outside Nigeria was in April 2012 in Pakistan,<ref name="GPEI_2015" /> and its absence from sewage monitoring in Pakistan suggests that active transmission of this strain has ceased there.<ref>{{cite news | vauthors = Choudary A |url=https://www.dawn.com/news/781594/pakistan-close-to-getting-rid-of-a-polio-virus-who |title=Pakistan close to getting rid of a polio virus: WHO |work=Dawn |date=27 January 2013 |access-date=29 March 2014 |archive-date=23 May 2013 |archive-url=https://web.archive.org/web/20130523183744/http://dawn.com/2013/01/27/pakistan-close-to-getting-rid-of-a-polio-virus-who/ |url-status=live }}</ref> A total of 416 wild-virus cases were reported in 2013, almost double the previous year.<ref name=GPEI_2015 /><ref name=GPEI_2013 />{{rp|6}} Of these, cases in endemic countries dropped from 197 to 160, while those in non-endemic countries jumped from 5 to 256.<ref name=GPEI_2015 /> This was due to outbreaks in Central Africa (focused in Cameroon), the Horn of Africa, and the Middle East (focused in Syria).<ref name=GPEI_2013>{{cite web |title=Annual Report 2013 |url=https://polioeradication.org/wp-content/uploads/2016/07/GPEI_AR2013_A4_EN.pdf |website=Global Polio Eradication Initiative |access-date=16 August 2024}}</ref>{{rp|6}}
In April 2013, a case of wild polio in Mogadishu was reported, the first in Somalia since 2007.<ref name="Somalia wild">{{cite web | vauthors = Callaway E |url=http://blogs.nature.com/news/2013/05/somalia-records-its-first-wild-polio-case-since-2007.html |title=Somalia records its first wild polio case since 2007 |work=Nature News Blog |date=13 May 2013 |access-date=30 September 2015 |archive-date=1 October 2015 |archive-url=https://web.archive.org/web/20151001154312/http://blogs.nature.com/news/2013/05/somalia-records-its-first-wild-polio-case-since-2007.html |url-status=live }}</ref> By October, over 170 cases had been reported in the country,<ref>{{cite news | title=Somalia hit by severe polio outbreak | website=BBC News | date=16 August 2013 | url=https://www.bbc.com/news/world-africa-23729121 | access-date=27 October 2019 | archive-date=5 December 2019 | archive-url=https://web.archive.org/web/20191205050735/https://www.bbc.com/news/world-africa-23729121 | url-status=live }}</ref> with more cases in neighboring Kenya and the Somali Region of Ethiopia.
Routine sewage monitoring in 2012 had detected a WPV1 strain of Pakistani origin in Cairo, sparking a major vaccination push there.<ref>{{cite news| vauthors = McNeil Jr DG |author-link=Donald G. McNeil Jr.|title=Egypt: Polio Virus Is Found in Cairo's Sewers|url=https://www.nytimes.com/2013/01/24/health/egypt-polio-virus-is-found-in-cairos-sewers.html|access-date=28 April 2013|newspaper=The New York Times|date=23 January 2013|archive-date=4 June 2013|archive-url=https://web.archive.org/web/20130604160905/http://www.nytimes.com/2013/01/24/health/egypt-polio-virus-is-found-in-cairos-sewers.html|url-status=live}}</ref> The strain spread to Israel, where there was widespread environmental detection, but like Egypt, no paralysis cases.<ref name="polio detected Israel">{{cite web |url=https://www.who.int/csr/don/2013_06_03/en/index.html |title=Poliovirus detected from environmental samples in Israel |publisher=World Health Organization (WHO) |date=3 June 2013 |access-date=30 September 2015 |archive-date=13 February 2014 |archive-url=https://web.archive.org/web/20140213071447/http://www.who.int/csr/don/2013_06_03/en/index.html }}</ref><ref name="polio Israel TOI">{{cite news| vauthors = Sterman A, Winer Jr S |title=More polio virus traces detected in Israel|url=http://www.timesofisrael.com/more-polio-virus-traces-detected-in-israel/|access-date=13 June 2013|newspaper=Times of Israel|date=12 June 2013|archive-date=11 July 2017|archive-url=https://web.archive.org/web/20170711234142/http://www.timesofisrael.com/more-polio-virus-traces-detected-in-israel/|url-status=live}}</ref><ref name="polio Israel NYT">{{cite news| vauthors = McNeil Jr DG |author-link=Donald G. McNeil Jr.|title=Polio Virus Discovered in Sewage From Israel|url=https://www.nytimes.com/2013/06/04/health/polio-virus-discovered-in-sewage-from-israel.html|access-date=3 June 2013|newspaper=The New York Times|date=7 June 2013|archive-date=4 June 2013|archive-url=https://web.archive.org/web/20130604080157/http://www.nytimes.com/2013/06/04/health/polio-virus-discovered-in-sewage-from-israel.html|url-status=live}}</ref> It had more severe consequences when it spread to neighboring Syria, with the total number of cases eventually reaching 35, the first outbreak there since 1999.<ref>{{cite news | title=Polio outbreak in Syria confirmed | website=BBC News | date=29 October 2013 | url=https://www.bbc.com/news/world-middle-east-24726592 | access-date=27 October 2019 | archive-date=11 December 2019 | archive-url=https://web.archive.org/web/20191211035339/https://www.bbc.com/news/world-middle-east-24726592 | url-status=live }}</ref><ref name="Syria polio linked Egypt">{{cite news| vauthors = Nebehay S |title=Polio strain in Syria originated in Pakistan, WHO confirms|url=https://www.nbcnews.com/health/polio-strain-syria-originated-pakistan-who-confirms-2D11577484|date=11 November 2013|access-date=12 November 2013|work=NBC News|archive-date=31 March 2019|archive-url=https://web.archive.org/web/20190331153107/https://www.nbcnews.com/health/polio-strain-syria-originated-pakistan-who-confirms-2D11577484|url-status=live}}</ref>
In April 2013, the WHO announced a new $5.5{{nbsp}}billion, 6-year cooperative plan (called the 2013–18 Polio Eradication and Endgame Strategic Plan) to eradicate polio from its last reservoirs. The plan called for mass immunization campaigns in the three remaining endemic countries, and also dictated a switch to inactivated virus injections, to avoid the risk of the vaccine-derived outbreaks that occasionally occur from use of the live-virus oral vaccine.<ref name="5.5 billion">{{cite web | vauthors = Beaubien J |url=https://www.npr.org/sections/health-shots/2013/04/26/178993960/a-5-5-billion-road-map-to-banish-polio-forever |title=A $5.5 Billion Road Map To Banish Polio Forever |work=NPR |date=26 April 2013 |access-date=30 September 2015 |archive-date=3 October 2015 |archive-url=https://web.archive.org/web/20151003141247/http://www.npr.org/sections/health-shots/2013/04/26/178993960/a-5-5-billion-road-map-to-banish-polio-forever |url-status=live }}</ref>
In 2014, there were 359 reported cases of wild poliomyelitis, spread over twelve countries. Pakistan had the most with 306, an increase from 93 in 2013, which was blamed on Al Qaeda and Taliban militants preventing aid workers from vaccinating children in rural regions of the country.<ref>{{cite report|title=Semi-Annual Status Report, January-June 2014|publisher=Global Polio Eradication Initiative (GPEI)|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2014Jan-Jun.pdf|access-date=11 June 2018|archive-date=29 June 2017|archive-url=https://web.archive.org/web/20170629071449/http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2014Jan-Jun.pdf|url-status=live}}</ref><ref>{{cite report|title=Semi-Annual Status Report, July-December 2014|publisher=Global Polio Eradication Initiative (GPEI)|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2014Jul-Dec.pdf|access-date=11 June 2018|archive-date=29 June 2017|archive-url=https://web.archive.org/web/20170629073511/http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2014Jul-Dec.pdf|url-status=live}}</ref> On 27 March 2014, the WHO announced the eradication of poliomyelitis in the South-East Asia Region, in which the WHO includes eleven countries: Bangladesh, Bhutan, North Korea, India, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, Thailand, and Timor-Leste.<ref name="eradication">{{cite press release| url =http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/| title =WHO South-East Asia Region certified polio-free| publisher =World Health Organization (WHO)| date =27 March 2014| access-date =27 March 2014| archive-date =27 March 2014| archive-url =https://web.archive.org/web/20140327235218/http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/}}</ref> With the addition of this region, the proportion of world population living in polio-free regions reached 80%.<ref name="eradication" /> The last case of wild polio in the South-East Asia Region was reported in India on 13 January 2011.<ref>{{cite web| url =http://www.searo.who.int/entity/immunization/topics/polio/eradication/sea-polio-free/en/| title =Polio-free certification: WHO South-East Asia| publisher =World Health Organization (WHO)| date =27 March 2014| access-date =27 March 2014| archive-url =https://web.archive.org/web/20140327032034/http://www.searo.who.int/entity/immunization/topics/polio/eradication/sea-polio-free/en/| archive-date =27 March 2014}}</ref>
thumb|right|Countries with polio cases in 2015
During 2015, 74 cases of wild poliomyelitis were reported worldwide, 54 in Pakistan and 20 in Afghanistan. There were 32 circulating vaccine-derived poliovirus (cVDPV) cases in 2015.<ref>{{cite report|title=Semi-Annual Status Report, January-June 2015|publisher=Global Polio Eradication Initiative (GPEI)|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2015Jan-Jun.pdf|access-date=11 June 2018|archive-date=12 June 2018|archive-url=https://web.archive.org/web/20180612141845/http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2015Jan-Jun.pdf|url-status=live}}</ref><ref>{{cite report|title=Semi-Annual Status Report, July-December 2015|publisher=Global Polio Eradication Initiative (GPEI)|url=http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2015Jul-Dec-2.pdf|access-date=11 June 2018|archive-date=10 November 2016|archive-url=https://web.archive.org/web/20161110043558/http://polioeradication.org/wp-content/uploads/2016/07/GPEI_StatusReport2015Jul-Dec-2.pdf|url-status=live}}</ref>
On 25 September 2015, the WHO declared that Nigeria was no longer considered endemic for wild polio virus,<ref name="WHO_Nigeria" /> with no reported case of wild polio virus having been reported since 24 July 2014.<ref name="GPEI_2015">{{Cite web|url=http://www.polioeradication.org/Portals/0/Document/Data&Monitoring/Wild_poliovirus_list_2010-2015_8SEP.pdf|title=Wild Poliovirus 2010–2015|date=9 September 2015|website=Global Polio Eradication Initiative (GPEI)|archive-url=https://web.archive.org/web/20150928032436/http://polioeradication.org/Portals/0/Document/Data%26Monitoring/Wild_poliovirus_list_2010-2015_8SEP.pdf|archive-date=28 September 2015|access-date=12 September 2015}}</ref> A WPV1 strain not seen in five years resurfaced in Nigeria the following year.<ref name="WHO_2018">{{Cite news|url=https://www.who.int/news-room/detail/11-08-2016-government-of-nigeria-reports-2-wild-polio-cases-first-since-july-2014|title=Government of Nigeria reports 2 wild polio cases, first since July 2014|work=World Health Organization (WHO)|access-date=25 August 2018|archive-date=6 September 2018|archive-url=https://web.archive.org/web/20180906024210/http://www.who.int/news-room/detail/11-08-2016-government-of-nigeria-reports-2-wild-polio-cases-first-since-july-2014|url-status=live}}</ref>
The WPV2 virus was declared eradicated in September 2015 as it had not been detected in circulation since 1999,<ref name="News stories"/> and WPV3 was declared eradicated in October 2019,<ref name="polioeradication.org"/> having last been detected in 2012. However, both types persist as circulating vaccine-derived strains, the product of years of evolution of the attenuated "live" virus (which makes up the oral vaccine) as it transmits from the vaccinated to the unvaccinated and circulates in an under-immunized community.<ref>{{Cite web|title=GPEI-Circulating vaccine-derived poliovirus|url=http://polioeradication.org/polio-today/polio-now/this-week/circulating-vaccine-derived-poliovirus/|url-status=live|archive-url=https://web.archive.org/web/20200228050752/http://polioeradication.org/polio-today/polio-now/this-week/circulating-vaccine-derived-poliovirus/|archive-date=28 February 2020|access-date=2020-06-30|quote=On very rare occasions, if a population is seriously under-immunized, there are enough susceptible children for the excreted vaccine-derived polioviruses to begin circulating in the community. If the vaccine-virus is able to circulate for a prolonged period of time uninterrupted, it can mutate and, over the course of 12-18 months, reacquire neurovirulence. These viruses are called circulating vaccine-derived polioviruses (cVDPV).}}</ref>
=== 2016–2020 === {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+Reported polio cases in 2016<ref name="WHO2014" /> center|alt=World map of polio cases in 2016 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type(s) |- | Pakistan |20 |1 |{{color|#f00|endemic}} |{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}} |- | Afghanistan ||13||0|| {{color|#f00|endemic}} || {{color|#f00|WPV1}} |- | Nigeria ||4||1||{{color|#f00|endemic}}||{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}} |- | Laos ||0||3||{{color|#00f|cVDPV only}}|| {{color|#00f|cVDPV1}} |- class="sortbottom" | '''Total''' ||37||5|| || |} {{stack end}}
Because cVDPV2 strains continued to arise from trivalent oral vaccine that included attenuated PV2, during 2016 this vaccine was replaced with a bivalent version lacking WPV2 as well as trivalent injected inactivated vaccine that cannot lead to cVDPV cases. This was expected to prevent new strains of cVDPV2 from arising and allow eventual cessation of WPV2 vaccination.<ref>{{Cite web |title=Global synchronisation and the switch |url=http://www.polioeradication.org/mediaroom/newsstories/Global-synchronisation-and-the-switch/tabid/526/news/1366/Default.aspx |archive-url=https://web.archive.org/web/20160515042223/http://www.polioeradication.org/mediaroom/newsstories/Global-synchronisation-and-the-switch/tabid/526/news/1366/Default.aspx |archive-date=15 May 2016 |access-date=14 April 2016 |website=Global Polio Eradication Initiative (GPEI)}}</ref> The resulting global use of the injectable vaccine caused shortages,<ref>{{cite news | vauthors = Branswell H |date=19 May 2017 |title=As hopes for polio eradication rise, the endgame gets complicated, and a vaccine runs short |publisher=Stat |url=https://www.statnews.com/2017/05/19/polio-vaccine-shortages/ |url-status=live |access-date=19 May 2017 |archive-url=https://web.archive.org/web/20180908013511/https://www.statnews.com/2017/05/19/polio-vaccine-shortages/ |archive-date=8 September 2018}}</ref> and led the WHO in April 2017 to recommend general use of the fIPV vaccination protocol, involving subcutaneous injection of a lower dose than used in the standard intramuscular delivery.<ref>{{cite news |date=28 April 2017 |title=WHO urges polio vaccine dose cut amid shortage |publisher=Business Insider |agency=Agence France-Presse |url=https://www.businessinsider.com/afp-who-urges-polio-vaccine-dose-cut-amid-global-shortage-2017-4 |url-status=live |access-date=28 October 2019 |archive-url=https://web.archive.org/web/20191028191811/https://www.businessinsider.com/afp-who-urges-polio-vaccine-dose-cut-amid-global-shortage-2017-4 |archive-date=28 October 2019}}</ref>
{{Clear}} {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Reported polio cases in 2017<ref name="WHO2014">{{cite web|url = http://apps.who.int/immunization_monitoring/en/diseases/poliomyelitis/case_count.cfm|title = Polio Case Count|date = 27 December 2017|access-date = 27 December 2017|publisher = World Health Organization (WHO)|archive-date = 16 August 2014|archive-url = https://web.archive.org/web/20140816115613/http://apps.who.int/immunization_monitoring/en/diseases/poliomyelitis/case_count.cfm|url-status = live}}</ref> center|alt=World map of polio cases in 2017 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type(s) |- |Afghanistan |14 |0 |{{color|#f00|endemic}} |{{color|#f00|WPV1}} |- |Pakistan |8 |0 |{{color|#f00|endemic}} |{{color|#f00|WPV1}} |- |Dem. Rep. Congo |0 |22 |{{color|#00f|cVDPV only}} |{{color|#00f|cVDPV2}} |- |Syria |0 |74 |{{color|#00f|cVDPV only}} |{{color|#00f|cVDPV2}} |- class="sortbottom" | '''Total''' ||22||96|| || |} {{stack end}}
In 2016 there were 37 reported WPV1 cases, half as many as in 2015, with the majority of the cases in Pakistan and Afghanistan.<ref>{{cite report|title=Global Polio Eradication Initiative Annual Report 2016|url=http://polioeradication.org/wp-content/uploads/2017/08/AR2016_EN.pdf|access-date=24 June 2018|publisher=Global Polio Eradication Initiative (GPEI)|archive-date=24 June 2018|archive-url=https://web.archive.org/web/20180624175300/http://polioeradication.org/wp-content/uploads/2017/08/AR2016_EN.pdf|url-status=live}}</ref> A small number of additional cases in Nigeria, caused by WPV1, were viewed as a setback, the first being detected there in almost two years, yet the virus had been circulating undetected in regions inaccessible due to the activities of Boko Haram.<ref name="WHO_2018" /><ref>{{cite news| vauthors = Okafor JL |title=How polio returned to Nigeria|url=https://www.dailytrust.com.ng/how-polio-returned-to-nigeria.html|date=11 August 2016|newspaper=Daily Trust|access-date=11 August 2016|archive-date=28 October 2019|archive-url=https://web.archive.org/web/20191028184407/https://www.dailytrust.com.ng/how-polio-returned-to-nigeria.html|url-status=live}}</ref> There was also a cVDPV1 outbreak in Laos,<ref>{{Cite web|url=https://www.who.int/csr/don/25-february-2016-polio-lao/en/|title=Circulating vaccine-derived poliovirus – Lao People's Democratic Republic|website=World Health Organization (WHO)|access-date=9 February 2017|archive-date=19 January 2017|archive-url=https://web.archive.org/web/20170119095130/http://www.who.int/csr/don/25-february-2016-polio-lao/en/}}</ref> while new strains of cVDPV2 arose separately in Nigeria's Borno and Sekoto states, and in the Quetta area of Pakistan,<ref>{{cite web|title=Semi-Annual Status Report: July to December 2016|url=http://polioeradication.org/wp-content/uploads/2017/04/Status-Report_Jul-Dec2016.pdf|publisher=Global Polio Eradication Initiative (GPEI)|page=8|access-date=28 April 2017|archive-date=28 April 2017|archive-url=https://web.archive.org/web/20170428052118/http://polioeradication.org/wp-content/uploads/2017/04/Status-Report_Jul-Dec2016.pdf|url-status=live}}</ref><ref>{{cite web|url=https://www.who.int/csr/don/27-december-2016-polio-pakistan/en/|title=Summary of poliovirus circulation in 2016 – Pakistan|publisher=World Health Organization (WHO)|date=27 December 2016|access-date=2 January 2017|archive-date=2 January 2017|archive-url=https://web.archive.org/web/20170102063839/http://www.who.int/csr/don/27-december-2016-polio-pakistan/en/}}</ref> collectively causing five cases.
{{clear}} {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Reported polio cases in 2018<ref name="GWP-Nov2020">{{cite web|url=http://polioeradication.org/wp-content/uploads/2020/11/weekly-polio-analyses-wpv-20201104.pdf|title=Global Wild Poliovirus 2015-2020 |date=3 November 2020|publisher=Global Polio Eradication Initiative (GPEI)|access-date=9 November 2020}}</ref><ref name="GcVDPV-Feb2021">{{cite web|url=https://polioeradication.org/wp-content/uploads/2021/02/weekly-polio-analyses-cVDPV-20210212.pdf|title=Global Circulating Vaccine-derived Poliovirus (cVDPV) |date=9 February 2021| publisher=Global Polio Eradication Initiative (GPEI)|access-date=12 February 2021}}</ref> center|alt=World map of polio cases in 2018 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- | Afghanistan |21 |0 |{{color|#f00|endemic}} |{{color|#f00|WPV1}} |- | Pakistan |12 |0 |{{color|#f00|endemic}} |{{color|#f00|WPV1}} |- | Nigeria ||0||34||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Papua New Guinea ||0||26||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- |Dem. Rep. Congo |0 |20 |{{color|#00f|cVDPV only}} |{{color|#00f|cVDPV2}} |- | Niger ||0||10||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Somalia ||0||6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2<br />cVDPV3}} |- | Indonesia ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | Mozambique ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- class="sortbottom" | '''Total''' ||33||98|| || |} {{stack end}} In 2017 there were 22 reported WPV1 polio cases with onset of paralysis in 2017, down from 37 in 2016. Eight of the cases were in Pakistan and 14 in Afghanistan,<ref name="GWP-Dec2022" /> where genetic typing showed repeated introduction from Pakistan as well as local transmission.<ref>{{cite journal | vauthors = Martinez M, Shukla H, Nikulin J, Wadood MZ, Hadler S, Mbaeyi C, Tangermann R, Jorba J, Ehrhardt D | title = Progress Toward Poliomyelitis Eradication - Afghanistan, January 2016-June 2017 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 66 | issue = 32 | pages = 854–858 | date = August 2017 | pmid = 28817551 | pmc = 5657670 | doi = 10.15585/mmwr.mm6632a5 | url = https://www.cdc.gov/mmwr/volumes/66/wr/pdfs/mm6632.pdf | access-date = 27 October 2019 | url-status = live | archive-url = https://web.archive.org/web/20190619093517/https://www.cdc.gov/mmwr/volumes/66/wr/pdfs/mm6632.pdf | archive-date = 19 June 2019 }}</ref> In Pakistan, transmission of several genetic lineages of WPV1 seen in 2015 had been interrupted by September 2017, though at least two genetic clusters remain. In spite of a significant drop in detected cases in Pakistan, there was an increase in the percentage of environmental samples that test positive for the polio virus, suggesting gaps in identification of infected individuals.<ref>{{cite journal | vauthors = Elhamidi Y, Mahamud A, Safdar M, Al Tamimi W, Jorba J, Mbaeyi C, Hsu CH, Wadood Z, Sharif S, Ehrhardt D | title = Progress Toward Poliomyelitis Eradication - Pakistan, January 2016-September 2017 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 66 | issue = 46 | pages = 1276–1280 | date = November 2017 | pmid = 29166363 | pmc = 5769788 | doi = 10.15585/mmwr.mm6646a4 }}</ref><ref>{{cite journal | vauthors = Roberts L | title='What the hell is going on?' Polio cases are vanishing in Pakistan, yet the virus won't go away | journal=Science | doi=10.1126/science.aas9789 | url=https://www.science.org/content/article/what-hell-going-polio-cases-are-vanishing-pakistan-yet-virus-wont-go-away | date=11 January 2018 | access-date=19 January 2018 | archive-date=17 January 2018 | archive-url=https://web.archive.org/web/20180117070449/http://www.sciencemag.org/news/2018/01/what-hell-going-polio-cases-are-vanishing-pakistan-yet-virus-wont-go-away | url-status=live | url-access=subscription }}</ref> In the third country where polio remained endemic, Nigeria, there were no cases, though as few as 7% of infants were fully vaccinated in some districts.<ref name="GWP-Dec2022" /><ref name=MMRWNigeria2018>{{cite journal | vauthors = Bolu O, Nnadi C, Damisa E, Braka F, Siddique A, Archer WR, Bammeke P, Banda R, Higgins J, Edukugo A, Nganda GW, Forbi JC, Liu H, Gidado S, Soghaier M, Franka R, Waziri N, Burns CC, Vertefeuille J, Wiesen E, Adamu U | title = Progress Toward Poliomyelitis Eradication - Nigeria, January-December 2017 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 67 | issue = 8 | pages = 253–256 | date = March 2018 | pmid = 29494568 | pmc = 5861699 | doi = 10.15585/mmwr.mm6708a5 }}</ref> An April 2017 spill at a vaccine production facility in the Netherlands only resulted in one asymptomatic WPV2 infection, despite release into the sewer system.<ref>{{cite journal | vauthors = Duizer E, Ruijs WL, van der Weijden CP, Timen A | title = Response to a wild poliovirus type 2 (WPV2)-shedding event following accidental exposure to WPV2, the Netherlands, April 2017 | journal = Euro Surveillance | volume = 22 | issue = 21 | article-number = 30542 | date = May 2017 | pmid = 28597830 | pmc = 5479986 | doi = 10.2807/1560-7917.ES.2017.22.21.30542 | author-link4 = Aura Timen }}</ref>
{{Clear}} {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Reported polio cases in 2019<ref name="GWP-Nov2020" /><ref name="GcVDPV-Nov2020">{{cite web|url=http://polioeradication.org/wp-content/uploads/2020/11/weekly-polio-analyses-cVDPV-20201104.pdf|title=Global Circulating Vaccine-derived Poliovirus (cVDPV) |date=3 November 2020| publisher=Global Polio Eradication Initiative (GPEI)|access-date=9 November 2020}}</ref> center|alt=World map of polio cases in 2019 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- | Pakistan||146||22||{{color|#f00|endemic}}||{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}} |- | Afghanistan||29||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Angola||0||138||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Dem. Rep. Congo||0||88||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Central African Rep.||0||21||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ghana ||0||18||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Nigeria ||0||18||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ethiopia ||0||14||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Philippines ||0||14||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1<br />cVDPV2}} |- | Chad ||0||11||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Benin ||0||8||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Togo ||0||8||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Myanmar ||0||6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | Somalia ||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Malaysia ||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | Zambia ||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Burkina Faso ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | China ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Niger ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Yemen ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | '''Total''' ||176||378|| || |} {{stack end}} Laos was declared free of cVDPV1 in March 2017,<ref name="WHO_Laos">{{cite press release|date= 6 March 2017|title= The poliovirus transmission in Lao People's Democratic Republic has ceased|url= http://www.wpro.who.int/laos/mediacentre/releases/2017/20170307-polio-transmission-lao-ceased/en/|publisher= World Health Organization (WHO)|access-date= 4 April 2017|archive-date= 31 October 2018|archive-url= https://web.archive.org/web/20181031221221/http://www.wpro.who.int/laos/mediacentre/releases/2017/20170307-polio-transmission-lao-ceased/en/|url-status= live}}</ref><ref>{{cite web|title=End of Outbreak in Lao Peoples Democratic Republic|publisher=Global Polio Eradication Initiative (GPEI)|date=29 May 2017|access-date=29 May 2017|url=http://polioeradication.org/news-post/end-of-outbreak-in-lao-peoples-democratic-republic/|archive-date=1 March 2019|archive-url=https://web.archive.org/web/20190301015739/http://polioeradication.org/news-post/end-of-outbreak-in-lao-peoples-democratic-republic/|url-status=live}}</ref> but three distinct cVDPV2 outbreaks occurred in the Democratic Republic of the Congo, one of them of recent origin, the other two having circulated undetected for more than a year. Together they caused 20 cases by year's end.<ref>{{cite web| vauthors = Herriman R |title=Polio update: Two cVDPV2 outbreaks reported in Democratic Republic of the Congo|publisher=Outbreak News Today|url=http://outbreaknewstoday.com/polio-update-two-cvdpv2-outbreaks-reported-democratic-republic-congo-39590/|date=25 May 2017|access-date=25 May 2017|archive-date=25 May 2017|archive-url=https://web.archive.org/web/20170525194827/http://outbreaknewstoday.com/polio-update-two-cvdpv2-outbreaks-reported-democratic-republic-congo-39590/}}</ref><ref>{{cite journal | vauthors = Alleman MM, Chitale R, Burns CC, Iber J, Dybdahl-Sissoko N, Chen Q, Van Koko DR, Ewetola R, Riziki Y, Kavunga-Membo H, Dah C, Andriamihantanirina R | title = Vaccine-Derived Poliovirus Outbreaks and Events - Three Provinces, Democratic Republic of the Congo, 2017 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 67 | issue = 10 | pages = 300–305 | date = March 2018 | pmid = 29543791 | pmc = 5857197 | doi = 10.15585/mmwr.mm6710a4 }}</ref><ref name=DRCWHO>{{cite web|title=Circulating vaccine-derived poliovirus type 2 – Democratic Republic of the Congo|publisher=World Health Organization (WHO)|date=10 July 2018|access-date=13 August 2018|url=https://www.who.int/csr/don/10-july-2018-polio-drc/en/|archive-date=28 August 2018|archive-url=https://web.archive.org/web/20180828231254/http://www.who.int/csr/don/10-july-2018-polio-drc/en/}}</ref><ref name=DRCHorn>{{cite journal | vauthors = Mbaeyi C, Alleman MM, Ehrhardt D, Wiesen E, Burns CC, Liu H, Ewetola R, Seakamela L, Mdodo R, Ndoutabe M, Wenye PK, Riziki Y, Borus P, Kamugisha C, Wassilak SG | title = Update on Vaccine-Derived Poliovirus Outbreaks - Democratic Republic of the Congo and Horn of Africa, 2017-2018 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 68 | issue = 9 | pages = 225–230 | date = March 2019 | pmid = 30845121 | pmc = 6421971 | doi = 10.15585/mmwr.mm6809a2 }}</ref> In Syria, a large outbreak began at Mayadin, Deir ez-Zor Governorate, a center of fighting in the Syrian Civil War, and also spreading to neighboring districts saw 74 confirmed cases from a viral strain that had circulated undetected for about two years.<ref name=Branswell-Syria>{{cite news| vauthors = Branswell H |title=Polio outbreak is reported in Syria, WHO says|publisher=STAT|date=8 June 2017|access-date=8 June 2017|url=https://www.statnews.com/2017/06/08/polio-outbreak-syria-who/|archive-date=8 June 2017|archive-url=https://web.archive.org/web/20170608170838/https://www.statnews.com/2017/06/08/polio-outbreak-syria-who/|url-status=live}}</ref><ref>{{cite news|title=WHO says child from Raqqa among 15 new polio cases in Syria|publisher=Reuters|url=https://www.reuters.com/article/us-mideast-crisis-syria-polio-idUSKBN19B1V8|date=20 June 2017|access-date=20 June 2017|archive-date=20 June 2017|archive-url=https://web.archive.org/web/20170620173515/http://www.reuters.com/article/us-mideast-crisis-syria-polio-idUSKBN19B1V8|url-status=live}}</ref> Circulation of multiple genetic lines of cVDPV2 was also detected in Banadir province, Somalia, but no infected individuals were identified.<ref name="WHO Somalia">{{cite web|title=Circulating vaccine-derived poliovirus type 2 – Somalia|date=9 March 2018|publisher=World Health Organization (WHO)|access-date=21 October 2018|url=https://www.who.int/csr/don/09-March-2018-polio-Somalia/en/|archive-date=20 October 2018|archive-url=https://web.archive.org/web/20181020135220/http://www.who.int/csr/don/09-March-2018-polio-Somalia/en/}}</ref> WHO's Strategic Advisory Group of Experts on Immunization recommended that cVDPV2 suppression be prioritized over targeting WPV1,<ref name="SAGEApr2017">{{Cite web |url=https://www.who.int/immunization/sage/meetings/2017/april/SAGE_April_2017_Meeting_Web_summary.pdf?ua=1 |title=Summary of the April 2017 meeting of the Strategic Advisory Group of Experts on Immunization |website=World Health Organization (WHO) |access-date=15 May 2017 |archive-date=5 March 2020 |archive-url=https://web.archive.org/web/20200305190823/https://www.who.int/immunization/sage/meetings/2017/april/SAGE_April_2017_Meeting_Web_summary.pdf?ua=1 |url-status=live }}</ref> and according to protocol OPV2 is restricted to this purpose.
{{Clear}} {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Reported polio cases in 2020<ref name="GWP-Mar2021">{{Cite web|url=https://polioeradication.org/wp-content/uploads/2021/03/weekly-polio-analyses-WPV-20210323.pdf|title=Global Wild Poliovirus 2016–2021|date=23 March 2021|website=GPEI|access-date=25 March 2021}}</ref><ref name=VDPVcurrent /> center|alt=World map of polio cases in 2020 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- |Pakistan||84||135||{{color|#f00|endemic}}||{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}} |- | Afghanistan ||56||308||{{color|#f00|endemic}}||{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}} |- | Chad||0||99||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Dem. Rep. Congo||0||81||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Burkina Faso ||0||65||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ivory Coast||0||61||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Sudan||0||58||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Mali ||0||52||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | South Sudan||0||50||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Guinea ||0||44||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ethiopia||0||36||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Yemen||0||31||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | Somalia||0||14||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ghana ||0||12||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Niger||0||10||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Sierra Leone ||0||10||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Togo ||0||9||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Nigeria ||0||8||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Cameroon ||0||7||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Central African Rep. ||0||4||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Angola ||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Benin ||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Rep. Congo ||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Madagascar ||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | Malaysia ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | Philippines ||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Tajikistan||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- class="sortbottom" | '''Total''' ||140||1107|| || |} {{stack end}}
There were 33 reported WPV1 paralysis cases with an onset of paralysis in 2018 – 21 in Afghanistan and 12 in Pakistan.<ref name="GWP-Dec2022" /><ref>{{Cite web|url=http://www.emro.who.int/pak/information-resources/polio-weekly-bulletins-2017.html|title=Weekly AFP surveillance updates: Pakistan|website=WHO Eastern Mediterranean Regional Office |access-date=24 January 2019|archive-date=14 January 2019|archive-url=https://web.archive.org/web/20190114042855/http://www.emro.who.int/pak/information-resources/polio-weekly-bulletins-2017.html|url-status=live}}</ref> Polio in Pakistan resurged in the latter part of the year,<ref name="IMB17">{{Cite report |url=http://polioeradication.org/wp-content/uploads/2016/07/17th-IMB-report-20191115.pdf |title=The Art of Survival: The Polio Virus Continues to Exploit Human Frailties. 17th Independent Monitoring Board Report |date=November 2019 |publisher=Global Polio Eradication Initiative |access-date=22 November 2019 |archive-url=https://web.archive.org/web/20191123004133/http://polioeradication.org/wp-content/uploads/2016/07/17th-IMB-report-20191115.pdf |archive-date=23 November 2019 |url-status=live}}</ref> due in part to the rates of parental refusal for vaccination increasing,<ref>{{cite journal | vauthors = Hsu C, Mahamud A, Safdar M, Nikulin J, Jorba J, Bullard K, Agbor J, Kader M, Sharif S, Ahmed J, Ehrhardt D | title = Progress Toward Poliomyelitis Eradication - Pakistan, January 2017-September 2018 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 67 | issue = 44 | pages = 1242–1245 | date = November 2018 | pmid = 30408024 | pmc = 6223954 | doi = 10.15585/mmwr.mm6744a5 }}</ref> with wild poliovirus detected in 20% of the year's environmental samples.<ref>{{Cite report|url=https://www.endpolio.com.pk/images/polio-briefer/Pakistan-Polio-Update-FEBRUARY-2019.pdf|title=Pakistan Polio Update, February 2019| publisher=Pakistan Polio Eradication Programme |date=February 2019}}</ref> In Afghanistan different strains were largely responsible for the cases in the northeast and south of the country.<ref name="Martinez2019">{{cite journal | vauthors = Martinez M, Shukla H, Nikulin J, Mbaeyi C, Jorba J, Ehrhardt D | title = Progress Toward Poliomyelitis Eradication - Afghanistan, January 2018-May 2019 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 68 | issue = 33 | pages = 729–733 | date = August 2019 | pmid = 31437144 | pmc = 6705892 | doi = 10.15585/mmwr.mm6833a4 | first9 = Derek }}</ref> In Nigeria, the third country classified as having endemic transmission, security concerns continued to limit access to some areas of the country, though migration and novel vaccination approaches would reduce the number of unreached children.<ref name="MMRWNigeria2018" /><ref name="MMWRNigeria2019">{{cite journal | vauthors = Adamu US, Archer WR, Braka F, Damisa E, Siddique A, Baig S, Higgins J, Sume GE, Banda R, Korir CK, Waziri N, Gidado S, Bammeke P, Edukugo A, Nganda GW, Forbi JC, Burns CC, Liu H, Jorba J, Asekun A, Franka R, Wassilak SG, Bolu O | title = Progress Toward Poliomyelitis Eradication - Nigeria, January 2018 – May 2019 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 68 | issue = 29 | pages = 642–646 | date = July 2019 | pmid = 31344023 | pmc = 6660103 | doi = 10.15585/mmwr.mm6829a3 }}</ref> The nation passed two full years without a detected wild-virus case, though elimination of WPV transmission could not be confirmed.<ref>{{cite press release|title=Nigeria not lowering guards against Polio, two years after last detection of cases in the Northeast|date=13 September 2018|publisher=WHO:Africa|url=https://www.afro.who.int/news/nigeria-not-lowering-guards-against-polio-two-years-after-last-detection-cases-northeast|access-date=22 November 2019|archive-date=23 November 2019|archive-url=https://web.archive.org/web/20191123004228/https://www.afro.who.int/news/nigeria-not-lowering-guards-against-polio-two-years-after-last-detection-cases-northeast|url-status=live}}</ref>
thumb|left|Polio vaccination in the Democratic Republic of Congo Cases caused by vaccine-derived poliovirus were reported in seven countries in 2018, with over 100 total cases, representing nine strains of cVDPV.<ref name="surv" /> In the Democratic Republic of the Congo, one of the outbreaks of cVDPV2 first detected in 2017 caused no additional cases, but suppression of the other two with OPV2 proved insufficient: not only did they continue, but the vaccination efforts gave rise to a novel cVDPV2 outbreak.<ref name="DRCHorn" /> The country experienced a total of 20 cases in 2018.<ref name="DRCWHO" /><ref name="GcVDPV-Oct2022">{{cite web |date=2022-10-11 |title=Global Circulating Vaccine-derived Poliovirus (cVDPV) |url=https://polioeradication.org/wp-content/uploads/2022/10/weekly-polio-analyses-cVDPV-20221011.pdf |url-status=live |archive-url=https://web.archive.org/web/20221016180851/https://polioeradication.org/wp-content/uploads/2022/10/weekly-polio-analyses-cVDPV-20221011.pdf |archive-date=2022-10-16 |access-date=2022-11-29 |website=GPEI}}</ref> Two separate cVDPV2 outbreaks in northern Nigeria produced 34 cases,<ref name="GcVDPV-Oct2022" /><ref>{{cite web|title=Circulating vaccine-derived poliovirus type 2 – Nigeria|publisher=World Health Organization (WHO)|date=8 August 2018|access-date=13 August 2018|url=https://www.who.int/csr/don/08-august-2018-polio-nigeria/en/|archive-date=12 August 2018|archive-url=https://web.archive.org/web/20180812162122/http://www.who.int/csr/don/08-august-2018-polio-nigeria/en/}}</ref> as well as giving rise to 10 cases in the neighboring Niger. In Somalia, cVDPV2 continued to circulate, causing several polio cases and detected in environmental samples from as far as Nairobi, Kenya. This virus, along with newly detected cVDPV3, caused twelve total cases in the country, including one patient infected by both strains.<ref name="GcVDPV-Oct2022" /><ref name="WHO Somalia" /><ref>{{cite report|title=Somalia cVDPV Outbreak Response Situation Report #3|publisher=WHO, UNICEF|date=20 August 2018|access-date=25 August 2018|url=https://reliefweb.int/sites/reliefweb.int/files/resources/WHO%20UNICEF%20Situation%20Report%20%233%20-%20Somalia%20cVDPV%20outbreak.pdf}}</ref> The large number of children residing in areas inaccessible to health workers represented a particular risk for undetected cVDPV outbreaks.<ref name="DRCHorn" /> A cVDPV2 outbreak in Mozambique resulted in a single case.<ref name="GcVDPV-Oct2022" /><ref>{{cite web | title=Polio outbreak confirmed in Mozambique | website=Global Polio Eradication Initiative (GPEI) | date=8 January 2019 | url=http://polioeradication.org/news-post/polio-outbreak-confirmed-in-mozambique/ | access-date=27 October 2019 | archive-date=23 October 2019 | archive-url=https://web.archive.org/web/20191023193435/http://polioeradication.org/news-post/polio-outbreak-confirmed-in-mozambique/ | url-status=live }}</ref> Response to the Syrian cVDPV2 outbreak continued into 2018, and virus transmission was successfully interrupted.<ref>{{cite journal | vauthors = Mbaeyi C, Wadood ZM, Moran T, Ather F, Stehling-Ariza T, Nikulin J, Al Safadi M, Iber J, Zomahoun L, Abourshaid N, Pang H, Collins N, Asghar H, Butt OU, Burns CC, Ehrhardt D, Sharaf M | title = Strategic Response to an Outbreak of Circulating Vaccine-Derived Poliovirus Type 2 - Syria, 2017-2018 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 67 | issue = 24 | pages = 690–694 | date = June 2018 | pmid = 29927908 | pmc = 6013082 | doi = 10.15585/mmwr.mm6724a5 }}</ref> In Papua New Guinea, a cVDPV1 strain arose, causing twenty-six polio cases across nine provinces,<ref>{{cite report |title=Papua New Guinea Polio Outbreak Response 2018 |publisher=World Health Organization (WHO) |year=2019 |url=https://reliefweb.int/sites/reliefweb.int/files/resources/9789290618867-eng.pdf |access-date=27 August 2020 |archive-date=27 August 2020 |archive-url=https://web.archive.org/web/20200827174627/https://reliefweb.int/sites/reliefweb.int/files/resources/9789290618867-eng.pdf |url-status=live }}</ref> while a single diagnosed cVDPV1 case in neighboring Indonesia<ref name="GcVDPV-Oct2022" /> resulted from a distinct outbreak.
{{Clear}} In 2019 there were 176 WPV1 paralysis cases detected: 29 in Afghanistan and 147 in Pakistan.<ref name="GWP-Dec2022" /> In particular, in Pakistan the number of cases was surging<ref>{{Cite journal|url=https://www.science.org/content/article/surging-cases-have-dashed-all-hope-polio-might-be-eradicated-2019|title=Surging cases have dashed all hope that polio might be eradicated in 2019| vauthors = Roberts L |date=10 July 2019|journal=Science|doi=10.1126/science.aay6925|s2cid=199264809|access-date=12 July 2019|archive-date=12 July 2019|archive-url=https://web.archive.org/web/20190712163846/https://www.sciencemag.org/news/2019/07/surging-cases-have-dashed-all-hope-polio-might-be-eradicated-2019|url-status=live|url-access=subscription}}</ref><ref name="calm">{{cite news| vauthors = McNeil Jr DG |author-link=Donald McNeil Jr.|title=To Calm Nervous Families, Pakistan Changes Polio Vaccination Tactics|work=The New York Times|date=24 May 2019|access-date=30 May 2019|url=https://www.nytimes.com/2019/05/24/health/pakistan-vaccination-polio.html|archive-date=29 May 2019|archive-url=https://web.archive.org/web/20190529185834/https://www.nytimes.com/2019/05/24/health/pakistan-vaccination-polio.html|url-status=live}}</ref> and cross-border migration played a role in polio transmission between the two countries.<ref>{{Cite web|url=https://www.who.int/news-room/detail/01-03-2019-statement-of-the-twentieth-ihr-emergency-committee|title=Statement of the Twentieth IHR Emergency Committee|website=World Health Organization (WHO)|access-date=16 March 2019|archive-date=12 March 2019|archive-url=https://web.archive.org/web/20190312032456/https://www.who.int/news-room/detail/01-03-2019-statement-of-the-twentieth-ihr-emergency-committee|url-status=live}}</ref><ref>{{cite news| vauthors = Nishat A |title=Polio spreads in Afghanistan and Pakistan 'due to unchecked borders'|work=The Guardian|url=https://www.theguardian.com/global-development/2019/feb/20/polio-spreads-in-afghanistan-and-pakistan-due-to-unchecked-borders|date=20 February 2019|access-date=20 February 2019|archive-date=20 February 2019|archive-url=https://web.archive.org/web/20190220070949/https://www.theguardian.com/global-development/2019/feb/20/polio-spreads-in-afghanistan-and-pakistan-due-to-unchecked-borders|url-status=live}}</ref> While itself problematic, this also fostered a dangerous false narrative in both nations, blaming the other for the presence and spread of polio in their own country.<ref>{{Cite web|url=http://polioeradication.org/wp-content/uploads/2018/11/20181105-16th-IMB-Report-FINAL.pdf|title=How to Cut a Long Story Short (Sixteenth Report of the Independent Monitoring Board)|publisher=Global Polio Eradication Initiative (GPEI)|date=October 2018|access-date=3 March 2019|archive-date=29 March 2019|archive-url=https://web.archive.org/web/20190329222701/http://polioeradication.org/wp-content/uploads/2018/11/20181105-16th-IMB-Report-FINAL.pdf|url-status=live}}</ref> Environmental sampling in Pakistan showed the virus' presence in eight urban areas, a setback officials attributed primarily to vaccine refusal.<ref>{{cite news | vauthors = Constable P, Khan HN |date=5 March 2019 |access-date=7 March 2019 |title=Pakistan, on verge of eradicating polio virus, faces human hurdles |newspaper=The Washington Post |url=https://www.washingtonpost.com/world/asia_pacific/pakistan-on-verge-of-eradicating-polio-virus-faces-human-hurdles/2019/03/04/8758b01c-353d-11e9-8375-e3dcf6b68558_story.html |archive-date=6 March 2019 |archive-url=https://web.archive.org/web/20190306202330/https://www.washingtonpost.com/world/asia_pacific/pakistan-on-verge-of-eradicating-polio-virus-faces-human-hurdles/2019/03/04/8758b01c-353d-11e9-8375-e3dcf6b68558_story.html |url-status=live }}</ref> Opponents to vaccination in Pakistan launched a series of attacks in April that left one vaccinator and two security men dead, while false rumors and hoax videos reporting vaccine toxicity also disrupted vaccination efforts there.<ref name="calm" /><ref>{{cite news | vauthors = Saifi S, Shah S |title=Pakistan's anti-vaccination movement leads to string of deadly attacks |work=CNN |date=26 April 2019 |access-date=26 April 2019 |url=https://www.cnn.com/2019/04/26/health/polio-worker-deaths-pakistan-intl/index.html |archive-date=26 April 2019 |archive-url=https://web.archive.org/web/20190426123107/https://www.cnn.com/2019/04/26/health/polio-worker-deaths-pakistan-intl/index.html |url-status=live }}</ref> Wild poliovirus of Pakistani origin<ref>{{cite web|url=http://www.cidrap.umn.edu/news-perspective/2019/05/four-new-polio-cases-pakistan-study-tackles-partial-dose-vaccination|title=Four new polio cases in Pakistan as study tackles partial-dose vaccination| vauthors = Schnirring L |date=17 May 2019|publisher=Center for Infectious Disease Research and Policy (CIDRAP)|access-date=17 May 2019|archive-date=17 May 2019|archive-url=https://web.archive.org/web/20190517213049/http://www.cidrap.umn.edu/news-perspective/2019/05/four-new-polio-cases-pakistan-study-tackles-partial-dose-vaccination|url-status=live}}</ref> also spread to Iran where it was detected in several environmental samples.<ref name="GWP-Dec2022" /> Overall, the eradication efforts in Pakistan and Afghanistan were characterized as having become a "horror show", undermined by "public suspicion, political infighting, mismanagement and security problems".<ref name="IMB17" /><ref>{{cite news | vauthors =Farmer B |title=Campaign to stamp out polio in remaining hot spots has become 'a horror story', report warns |publisher=The Telegraph |date=20 November 2019 |access-date=21 November 2019 |url=https://www.telegraph.co.uk/global-health/science-and-disease/campaign-stamp-polio-remaining-hot-spots-has-become-horror-story/ |archive-date=23 December 2019 |archive-url=https://web.archive.org/web/20191223231050/https://www.telegraph.co.uk/global-health/science-and-disease/campaign-stamp-polio-remaining-hot-spots-has-become-horror-story/ |url-status=live }}</ref>
In the third remaining country in which polio was classified as endemic, Nigeria, wild poliovirus had not been detected since October 2016, and levels of AFP surveillance were sufficient, even in security-compromised regions, to suggest transmission of WPV might have been interrupted.<ref name="MMWRNigeria2019" /> Global WPV3 eradication was certified in October 2019, the virus not having been seen since 2012.<ref name=WPV3gone />
In addition to the WPV resurgence in Pakistan and Afghanistan, 2019 saw a resurgence of cVDPV, with 378 cases.<ref name="GcVDPV-Oct2022" /> The majority of cases were caused by cVDPV2 strains that were able to arise or spread as a consequence of the withdrawal of the PV2 strain from the standard vaccination regimen. Previous cVDPV2 outbreaks in Nigeria, the Democratic Republic of Congo, and Somalia continued into 2019 and spread to neighboring countries, while several countries experienced new outbreaks.<ref>{{Cite web|url=https://www.thenewhumanitarian.org/maps-and-graphics/2019/10/24/polio-outbreaks-how-virus-spread-decades-eradication-efforts|title=Mapped: Where polio lives in 2019|date=24 October 2019|website=The New Humanitarian|access-date=2 November 2019|archive-date=2 November 2019|archive-url=https://web.archive.org/web/20191102100730/https://www.thenewhumanitarian.org/maps-and-graphics/2019/10/24/polio-outbreaks-how-virus-spread-decades-eradication-efforts|url-status=live}}</ref> In addition to eighteen reported paralysis cases in Nigeria, the cVDPV2 outbreaks there spread to Benin, Burkina Faso, Chad, Ghana, Niger, and Togo, while the virus was also detected in environmental samples from Cameroon and Ivory Coast. Somalia's continuing outbreaks caused a half-dozen cases there and in neighboring Ethiopia, with a separate Ethiopia outbreak adding one case. The Democratic Republic of the Congo had numerous new and continuing outbreaks, producing more than 80 cases, while multiple new cVDPV2 outbreaks in Angola and the Central African Republic resulted in more than a hundred cases.<ref>{{cite report|title=Circulating vaccine-derived poliovirus type 2 – African Region|date=31 July 2019|access-date=3 August 2019|publisher=World Health Organization (WHO)|url=https://www.who.int/csr/don/31-july-2019-polio-africa-region/en/|archive-date=20 October 2019|archive-url=https://web.archive.org/web/20191020142004/https://www.who.int/csr/don/31-july-2019-polio-africa-region/en/}}</ref> Individual new outbreaks of cVDPV2 also caused more than a dozen paralysis cases each in Pakistan<ref name="GcVDPV-Oct2022" /> and the Philippines,<ref>{{cite news|url=https://www.cnn.com/2019/09/19/health/philippines-polio-outbreak-intl/index.html|title=Polio makes a comeback in the Philippines 19 years after the country was declared free of the disease| vauthors = Hunt K |date=19 September 2019|work=CNN|access-date=19 September 2019|archive-date=19 September 2019|archive-url=https://web.archive.org/web/20190919133847/https://www.cnn.com/2019/09/19/health/philippines-polio-outbreak-intl/index.html|url-status=live}}</ref><ref>{{cite news|url=https://www.upi.com/Top_News/World-News/2019/09/19/Labs-confirm-1st-new-case-of-polio-in-Philippines-in-26-years/8161568905986/|title=Labs confirm 1st new case of polio in Philippines in 26 years| vauthors = Clyde H |date=19 September 2019|publisher=United Press International (UPI)|access-date=19 September 2019|archive-date=20 September 2019|archive-url=https://web.archive.org/web/20190920051118/https://www.upi.com/Top_News/World-News/2019/09/19/Labs-confirm-1st-new-case-of-polio-in-Philippines-in-26-years/8161568905986/|url-status=live}}</ref> while smaller outbreaks struck Chad, China, and Zambia.<ref name="GcVDPV-Oct2022" /> A separate cVDPV1 outbreak in the Philippines also caused cases in Malaysia, where cVDPV2 of Filipino origin was also detected in environmental samples, while additional cVDPV1 outbreaks caused six cases in Myanmar and one case in Yemen.<ref name="GcVDPV-Oct2022" />
In March 2020, the GPEI announced polio eradication resources were being redeployed against the COVID-19 pandemic, recognizing that this would adversely affect its efforts at eradicating polio.<ref>{{cite press release|title=GPEI statement on COVID-19|publisher=GPEI|date=18 March 2020|access-date=21 March 2020|url=http://polioeradication.org/news-post/global-polio-eradication-initiative-statement-on-covid-19/|archive-date=21 March 2020|archive-url=https://web.archive.org/web/20200321214030/http://polioeradication.org/news-post/global-polio-eradication-initiative-statement-on-covid-19/|url-status=live}}</ref> All vaccination efforts, both routine and targeted, were postponed for several months,<ref>{{cite news | vauthors = Roberts L |title='We have no choice.' Pandemic forces polio eradication group to halt campaigns |date=1 April 2020 |access-date=7 April 2020 |work=Science |url=https://www.science.org/content/article/we-have-no-choice-pandemic-forces-polio-eradication-group-halt-campaigns |archive-date=6 April 2020 |archive-url=https://web.archive.org/web/20200406055449/https://www.sciencemag.org/news/2020/04/we-have-no-choice-pandemic-forces-polio-eradication-group-halt-campaigns |url-status=live }}</ref> with staff reassigned to COVID-19 control. Subsequent statistical analysis indicated that the COVID pandemic resulted in decreases of more than 30% globally in both AFP and environmental surveillance,<ref>{{cite journal | vauthors = Zomahoun DJ, Burman AL, Snider CJ, Chauvin C, Gardner T, Lickness JS, Ahmed JA, Diop O, Gerber S, Anand A | title = Impact of COVID-19 Pandemic on Global Poliovirus Surveillance | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 69 | issue = 5152 | pages = 1648–1652 | date = January 2021 | pmid = 33382673 | pmc = 9191906 | doi = 10.15585/mmwr.mm695152a4 | s2cid = 229942127 | doi-access = free }}</ref> with only 23 of 43 priority countries meeting their surveillance targets for 2020.<ref name="2022surveil">{{cite journal | vauthors = Wilkinson AL, Diop OM, Jorba J, Gardner T, Snider CJ, Ahmed J | title = Surveillance to Track Progress Toward Polio Eradication - Worldwide, 2020-2021 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 71 | issue = 15 | pages = 538–544 | date = April 2022 | pmid = 35421079 | pmc = 9020859 | doi = 10.15585/mmwr.mm7115a2 }}</ref> Additional challenges were a conspiracy theory circulating on social media claiming that the polio vaccine contained coronavirus, and moves by President Donald Trump of the United States to cut funding for the World Health Organization.<ref>{{Cite news| vauthors = Rauhala E, Paquette D, George S |title=Polio was almost eradicated. Then came the coronavirus. Then came a threat from President Trump|url=https://www.washingtonpost.com/world/polio-was-almost-eradicated-then-came-the-coronavirus-then-came-a-threat-from-president-trump/2020/05/15/ed9d26fe-831c-11ea-81a3-9690c9881111_story.html|url-status=live|archive-url=https://web.archive.org/web/20200701014250/https://www.washingtonpost.com/world/polio-was-almost-eradicated-then-came-the-coronavirus-then-came-a-threat-from-president-trump/2020/05/15/ed9d26fe-831c-11ea-81a3-9690c9881111_story.html|archive-date=1 July 2020|access-date=2020-07-01|newspaper=The Washington Post}}</ref>
Nigeria was removed from the list of countries with endemic wild poliovirus in June 2020,<ref>{{cite news | vauthors = Essien G |title=Stakeholders celebrate Nigeria's polio-free status |date=20 June 2020 |url=https://www.von.gov.ng/stakeholders-celebrate-nigerias-polio-free-status/ |access-date=18 July 2020 |archive-date=3 September 2020 |archive-url=https://web.archive.org/web/20200903165818/https://www.von.gov.ng/stakeholders-celebrate-nigerias-polio-free-status/ |url-status=live |newspaper=Voice of Nigeria}}</ref> four years after the last recorded case in the Northern State of Borno in 2016.<ref>{{cite news |title=Africa declared free of wild polio in 'milestone' |url=https://www.bbc.co.uk/news/world-africa-53887947 |work=BBC News |date=25 August 2020}}</ref> Two months later, the World Health Organization declared the African continent free of wild poliovirus.<ref name="Scherbel-Ball_2020">{{Cite news| vauthors = Scherbel-Ball N |date=2020-08-25|title=Africa declared free of polio|language=en-GB|work=BBC News|url=https://www.bbc.com/news/world-africa-53887947|access-date=2020-08-25|archive-date=26 August 2020|archive-url=https://web.archive.org/web/20200826154956/https://www.bbc.com/news/world-africa-53887947|url-status=live}}</ref> This certification came after extensive assessments of the certifications of National Polio Certification Commissions (NCCs)<ref name="cert">{{Cite web |date=2020-08-25 |title=Polio certification |url=https://www.afro.who.int/health-topics/polio/polio-certification |access-date=2020-08-25 |website=WHO Regional Office for Africa |language=en |archive-date=25 August 2020 |archive-url=https://web.archive.org/web/20200825071342/https://www.afro.who.int/health-topics/polio/polio-certification |url-status=live }}</ref> and confirmation that at least 95% of Africa's population had been immunised.<ref name="Scherbel-Ball_2020" /> WHO Director-General Tedros Adhanom called it a "great day... but not the end of polio",<ref>{{Cite news | vauthors = Godoy M |date=25 August 2020 |title=Africa Declares Wild Polio Is Wiped Out – Yet It Persists In Vaccine-Derived Cases |language=en |work=NPR |url=https://www.npr.org/sections/goatsandsoda/2020/08/25/905884740/africa-declares-wild-polio-is-wiped-out-yet-it-persists-in-vaccine-derived-cases |access-date=2020-08-25 |archive-date=25 August 2020 |archive-url=https://web.archive.org/web/20200825211106/https://www.npr.org/sections/goatsandsoda/2020/08/25/905884740/africa-declares-wild-polio-is-wiped-out-yet-it-persists-in-vaccine-derived-cases |url-status=live }}</ref> as there remain major continuing outbreaks of vaccine-derived poliovirus in West Africa and Ethiopia in addition to wild cases in Afghanistan and Pakistan.<ref name="25th EHRC">{{cite press release |title=Statement of the twenty-fifth polio IHR Emergency Committee |date=23 June 2020 |publisher=WHO |url=https://www.who.int/news-room/detail/23-06-2020-statement-of-the-25th-polio-ihr-emergency-committee |access-date=18 July 2020 |archive-date=15 July 2020 |archive-url=https://web.archive.org/web/20200715203155/https://www.who.int/news-room/detail/23-06-2020-statement-of-the-25th-polio-ihr-emergency-committee |url-status=live}}</ref>
Over 1,000 cases of cVDPV2 were reported in 2020 across twenty-four countries, caused by both continuing and novel outbreaks, with 31 additional cases of cVDPV1 and environmental detection in several additional countries with no diagnosed polio cases.<ref name="VDPVcurrent" /> While in the past cVDPV outbreaks tended to be localized, significant international spread was observed of these strains.<ref name="25th EHRC" /> {{Clear}}
=== 2021 === {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Confirmed polio cases in 2021<ref name="WPVcurrent" /><ref name="VDPVcurrent" /> frameless|center|alt=World map of polio cases in 2021 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- | Afghanistan||4||43||{{color|#f00|endemic}}||{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}} |- | Malawi||1||0||{{color|green|reintroduced}}||{{color|#f00|WPV1}} |- | Pakistan||1||8||{{color|#f00|endemic}}||{{color|#f00|WPV1}}<br />{{color|#00f|cVDPV2}} |- | Nigeria||0||418||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Yemen||0||69||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}}<br />{{color|#00f|cVDPV2}} |- | Tajikistan||0||35||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Dem. Rep. Congo||0||28||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Niger||0||18||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Senegal||0||17||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Madagascar||0||14||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV1}} |- | Ethiopia||0||10||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | South Sudan||0||9||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Guinea||0||6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Sierra Leone||0||5||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Benin||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Cameroon||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Guinea-Bissau||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Liberia||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Burkina Faso||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Mozambique||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Rep. Congo||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ukraine||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Eritrea||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Somalia||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- class="sortbottom" | '''Total'''||6||688|| || |} {{stack end}}In 2021, there were just six confirmed cases of wild poliovirus – one in Pakistan, four in Afghanistan, and one in Malawi.<ref name="WPVcurrent" />
2021 saw a partial recovery from the challenges to monitoring brought on by the COVID pandemic, with 74% of high-priority countries meeting surveillance targets, an improvement of over 20% from the previous year.<ref name="2022surveil" /> March 2021 also saw the first use of the modified nOPV2 vaccine in selected countries, engineered to allow vaccination against strain{{nbsp}}2 poliovirus without the frequent spawning of cVDPV2 seen with the original OPV2. Full rollout was not expected until 2023.<ref name="nOPV2release">{{cite press release |title=Independent experts advise move to next use phase for novel oral polio vaccine type 2 |publisher=GPEI |date=11 Oct 2021 |url=https://polioeradication.org/news-post/independent-experts-advise-transition-to-next-use-phase-for-novel-oral-polio-vaccine-type-2-nopv2/}}</ref>
Despite previous resistance to eradication efforts, after their takeover of Afghanistan in 2021 the Taliban agreed to allow United Nations healthcare workers to carry out door-to-door vaccination nationwide for the first time in three years, including a commitment to allowing women to participate in the effort, and to provide safety guarantees to eradication staff.<ref>{{cite news| vauthors = Sullivan B | title=Taliban will allow a national polio vaccination campaign in Afghanistan, says WHO| publisher=National Public Radio| date=19 October 2021| access-date=2021-10-19| url=https://www.npr.org/sections/goatsandsoda/2021/10/19/1047367660/taliban-will-allow-a-national-polio-vaccination-campaign-in-afghanistan-says-who}}</ref> Pakistan's lone case dated from January, but the virus continued to be detected in environmental samples through December,<ref name="WPVcurrent" /> and was present in most provinces of the country during the year.<ref>{{cite report |title=Pakistan Polio Update, September 2021 |date=September 2022 |publisher=Pakistan Polio Eradication Programme |url=https://www.endpolio.com.pk/images/polio-briefer/Pakistan-Polio-Update-September-2021.pdf |archive-date=21 January 2022 |access-date=28 January 2022 |archive-url=https://web.archive.org/web/20220121105226/https://www.endpolio.com.pk/images/polio-briefer/Pakistan-Polio-Update-September-2021.pdf |url-status=dead }}</ref> The reemergence of wild poliovirus in Malawi, the country's first case in almost three decades and the first in Africa in five years, was seen as a significant setback to the eradication effort.<ref name="GPEI-Malawi">{{cite press release| title=GPEI Statement on WPV1 in Malawi: Wild poliovirus type 1 detected in Lilongwe, Malawi |publisher=GPEI | date=2022-02-17| url=https://polioeradication.org/news-post/gpei-statement-on-wpv1-in-malawi/}}</ref><ref>{{cite news|title=Malawi finds Africa's first wild polio case in five years|work=BBC News |date=2022-02-18|access-date=2022-02-18|url=https://www.bbc.com/news/world-africa-60429726}}</ref><ref name="Science-Malawi">{{cite web| vauthors = Roberts L |title=In new setback for eradication campaign, poliovirus from Pakistan shows up in Africa: Health officials hope to squash outbreak quickly |work=Science |date=2022-02-17|access-date=2022-02-18|url=https://www.science.org/content/article/new-setback-eradication-campaign-poliovirus-pakistan-shows-africa}}</ref> Based on similarity to a strain last detected in Pakistan in 2019, it was thought that WPV1 had been circulating undetected in the country for some time.<ref name="Science-Malawi" />
In 2021, reported cVDPV2 cases declined to 685 across 22 countries, over half occurring in Nigeria. The virus was also found in environmental samples or in those from symptom-free people in several additional African and Asian nations without reported cases.<ref name="VDPVcurrent" /> An analysis of cVDPV2 strains from 2020 and the first half of 2021 attributed them to 38 distinct emergences, representing a mix of novel strains and previously detected strains that continued to circulate, while several previously circulating strains were no longer found.<ref name="MMWR2021cVDPV">{{cite journal | vauthors = Alleman MM, Jorba J, Henderson E, Diop OM, Shaukat S, Traoré MA, Wiesen E, Wassilak SG, Burns CC | title = Update on Vaccine-Derived Poliovirus Outbreaks – Worldwide, January 2020 – June 2021 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 70 | issue = 49 | pages = 1691–1699 | date = December 2021 | pmid = 34882653 | pmc = 8659190 | doi = 10.15585/mmwr.mm7049a1 }}</ref> 14 cases of cVDPV1 were identified in Madagascar and 3 in Yemen. No cases of cVDPV3 were observed, though it was detected in environmental samples from China and from Israel and its occupied territories.<ref name="VDPVcurrent" /><ref name="MMWR2021cVDPV" /> {{Clear}}
===2022=== {{Update after|2027|reason=This range should be closed on the announcement of Polio Eradication, or a major change in programme operations}} {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Confirmed polio cases in 2022<ref name="WPVcurrent" /><ref name="VDPVcurrent" /> frameless|center|alt=World map of polio cases in 2022 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- | Pakistan||20||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Mozambique||8<br/><br/>||<br/>22<br/>4||{{color|green|imported}}||{{color|#f00|WPV1}}<br />{{color|#80f|cVDPV1}}<br />{{color|#00f|cVDPV2}} |- | Afghanistan||2||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Dem. Rep. Congo||0||149<br/>372||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}}<br/>{{color|#00f|cVDPV2}} |- | Yemen||0||162||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Nigeria||0||48||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Chad||0||44||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Madagascar||0||16||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Niger||0||16||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Benin||0||13||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Central African Republic||0||6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Somalia||0||5||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Malawi||0||4||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Algeria||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Cameroon||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ghana||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Mali||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Togo||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Burundi||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Eritrea||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ethiopia||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Indonesia||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Israel||0||1||{{color|#00f|cVDPV only}}||{{color|#b04|cVDPV3}} |- | Rep. Congo||0||1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Sudan||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | United States||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- class="sortbottom" | '''Total'''||30||880|| || |} {{stack end}}
In 2022, there were 30 confirmed cases of WPV1 reported to WHO, with 2 and 20 cases in Pakistan and Afghanistan respectively, while eight non-endemic cases were recorded in Mozambique,<ref name="WPVcurrent" /> the first cases in the country since 1992. The Mozambique cases derived from the strain of Pakistani origin that caused two confirmed cases in Malawi in 2021.<ref>{{cite press release |title=GPEI statement on Mozambique WPV1 detection |date=2022-05-18 |publisher=GPEI |url=https://polioeradication.org/news-post/gpei-statement-on-mozambique-wpv1-detection/}}</ref> The cases in Pakistan were the first seen in the country in 15 months,<ref>{{cite news | vauthors = Gul A |title=Pakistan Detects First Polio Case in 15 Months |work=Voice of America |url=https://www.voanews.com/a/6542157.html |date=23 April 2022 |access-date=29 April 2022}}</ref> though the virus had been detected in environmental samples during the intervening period.<ref>{{cite news| vauthors = Gul A |title=WHO Cautions Against Complacency as Pakistan Marks Polio-Free Year |date=2022-01-28 |work=Voice of America |url=https://www.voanews.com/a/who-cautions-against-complacency-as-pakistan-marks-polio-free-year-/6416622.html |access-date=2022-01-28}}</ref>
The residual effects of the COVID-19 pandemic continued to be a cause for concern, due to an increased risk of undetected outbreaks due to COVID's interference with routine health care, disease detection, and childhood vaccinations, as well as a concern that an increased fear of vaccines, caused at least in part by politicization of vaccination and bad governance during the pandemic, might result in a general pattern of undervaccination, including for polio.<ref>{{cite web | vauthors = Kenen J |date=2022-03-28 |title=Polio's back. Blame Covid. |url=https://www.politico.com/newsletters/politico-nightly/2022/03/28/polios-back-blame-covid-00020977 |access-date=2022-04-02 |work=Politico}}</ref> In Pakistan, a contributing factor to the resurgence of wild virus cases in the country was threats of violence both from those with anti-vaccine sentiment and from religious extremists. A vaccination worker was assassinated in March 2022,<ref>{{cite news |date=2022-06-21 |title=Pakistan's fight against polio threatened by extremist violence, anti-vaccine sentiments |work=CBC News |url=https://www.cbc.ca/radio/thecurrent/the-current-for-june-20-2022-1.6494454/pakistan-s-fight-against-polio-threatened-by-extremist-violence-anti-vaccine-sentiments-1.6495629 |access-date=2022-06-24}}</ref> and a vaccinator and two accompanying police officers providing security for a door-to-door vaccination campaign were murdered in June.<ref>{{cite news |date=2022-06-28 |title=Gunmen in northwest Pakistan kill polio worker, two policemen |work=Al Jazeera |url=https://www.aljazeera.com/news/2022/6/28/gunmen-in-northwest-pakistan-kill-polio-worker-two-policemen |access-date=2022-06-30}}</ref> However, the situation had improved compared to previous years as the government and law enforcement increased their focus. By October 2022, endemic transmission was restricted to seven districts in southern Khyber Pakhtunkhwa, and the number of circulating genetic clusters was down to one, from eleven in 2020.<ref>{{cite web | title = Meeting of the Technical Advisory Group (TAG) on Poliomyelitis Eradication in Pakistan | date = 4 October 2022 | url = http://polioeradication.org/wp-content/uploads/2023/05/TAG-meeting-report-Pakistan-Muscat-Oman-4-6-October-2022-FOR-PRINT.pdf | location = Muscat, Oman | work = Global Polio Eradication Initiative | publisher = World Health Organization}}</ref>
The situation improved in Afghanistan as well, as between 2021 and 2022 the country became significantly more peaceful as the government consolidated their control, though with remaining pockets of violence.<ref>{{cite web | url=https://www.crisisgroup.org/asia/south-asia/afghanistan/afghanistans-security-challenges-under-taliban | title=Afghanistan's Security Challenges under the Taliban | date=12 August 2022 }}</ref>
Vaccine-derived cases continue to circulate, particularly in the African and Eastern Mediterranean WHO regions. Concern was focused on Ukraine, where cVDPV had been detected in fall 2021 but vaccination efforts had been halted due to the Russian invasion,<ref>{{cite news | vauthors = Abbott B, McKay B |date=2022-04-02 |title=Ukraine War and Other Crises Threaten Polio Eradication, Health Experts Say |newspaper=Wall Street Journal |url=https://www.wsj.com/articles/ukraine-war-and-other-crises-threaten-polio-eradication-health-experts-say-11648900800 |url-access=subscription |access-date=2022-04-02}}</ref> and on poor quality surveillance extant in Southeast Africa<ref>{{cite journal |date=2 June 2023 |title=Full issue |url=https://apps.who.int/iris/handle/10665/368486 |journal=Weekly Epidemiological Record |language=en |volume=98 |issue=22 |pages=239–256|hdl=10665/368486 }}</ref> 684 confirmed cases of cVDPV2 were seen across twenty countries during 2022, in addition to 189 cases of cVDPV1 and one case of cVDPV3 in Israel. The first case was reported in the United States since 2013,<ref name="new_york_doh">{{cite press release |title=New York State Department of Health and Rockland County Department of Health Alert the Public to A Case of Polio In the County |publisher=New York State Department of Health |url=https://www.health.ny.gov/press/releases/2022/2022-07-21_polio_rockland_county.htm |date=2022-07-21 |access-date=2022-07-21 |url-status=live |archive-url=https://web.archive.org/web/20220721174859/https://www.health.ny.gov/press/releases/2022/2022-07-21_polio_rockland_county.htm |archive-date=2022-07-21}}</ref> tied to cVDPV2 strains found in Israel and the United Kingdom.<ref name="reuters_new_york">{{cite news | vauthors = Heavey S |date=2022-08-01 |title=Polio found in New York wastewater as state urges vaccinations |newspaper=Reuters |url=https://www.reuters.com/world/us/polio-found-new-york-wastewater-state-assesses-virus-spread-2022-08-01/ |url-status=live |access-date=2022-08-01 |archive-url=https://web.archive.org/web/20220801234556/https://www.reuters.com/world/us/polio-found-new-york-wastewater-state-assesses-virus-spread-2022-08-01/ |archive-date=2022-08-01}}</ref> In Burundi and the Democratic Republic of the Congo, two outbreaks of cVDPV2 that caused a combined seven cases were identified as having a link to the nOPV2 vaccine, the first outbreaks with ties to nOPV2 after its initial deployment in 2021;<ref name="GPEI_Burundi">{{cite press release |title=GPEI Statement on cVDPV2 detections in Burundi and Democratic Republic of the Congo |publisher=Global Polio Eradication Initiative |url=https://polioeradication.org/news-post/gpei-statement-on-cvdpv2-detections-in-burundi-and-democratic-republic-of-the-congo/ |date=2023-03-16 |access-date=2023-03-17 |url-status=live |archive-url=https://web.archive.org/web/20230317014344/https://polioeradication.org/news-post/gpei-statement-on-cvdpv2-detections-in-burundi-and-democratic-republic-of-the-congo/ |archive-date=2023-03-17}}</ref><ref name="AP_Burundi">{{cite news | vauthors = Cheng M |date=2023-03-17 |title=Burundi officials detect polio outbreak linked to vaccine |newspaper=AP News |url=https://apnews.com/article/polio-burundi-epidemic-africa-vaccine-d7489fbf1bd75f8612672414d9a5f2c0 |url-status=live |access-date=2023-03-17 |archive-url=https://web.archive.org/web/20230317234457/https://apnews.com/article/polio-burundi-epidemic-africa-vaccine-d7489fbf1bd75f8612672414d9a5f2c0 |archive-date=2023-03-17}}</ref> according to an assessment reported by the GPEI, an estimated 30–40 additional outbreaks of cVDPV2 would have occurred from March 2021 to March 2023 without the nOPV2 rollout.<ref name="GPEI_Burundi" /> Vaccine-derived viral strains were also detected in environmental samples from a number of additional countries without diagnosed cases.<ref name="VDPVcurrent" /><ref>{{Cite web | vauthors = Cheng M | date = 21 August 2022 |title=Polio in US, UK and Israel reveals rare risk of oral vaccine |url=https://apnews.com/article/polio-oral-vaccine-linked-to-rare-infection-risk-db2b278b7e4f9fea9a2df48b8508ed14 |access-date=2022-08-21 |website=AP News |language=en}}</ref> From February to May, traces of cVDPV2 were discovered in sewage in London, United Kingdom. This led the United Kingdom to declare a "national incident". However, authorities have said that the risk to the general public is "extremely low", and no cases were reported.<ref>{{Cite news |date=2022-06-23 |title=U.K. declares 'national incident' after 'vaccine derived' polio strain found in sewage |language=en |work=National Post |publisher=The Associated Press |url=https://nationalpost.com/news/world/polio-virus-found-in-uk-sewage-samples-risk-to-public-low |access-date=2022-06-24}}</ref><ref>{{cite press release |title=Poliovirus detected in sewage from North and East London |publisher=UK Health Security Agency |date=22 June 2022 |url=https://www.gov.uk/government/news/poliovirus-detected-in-sewage-from-north-and-east-london}}</ref> {{Clear}}
=== 2023 === {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Confirmed polio cases in 2023<ref name="WPVcurrent" /><ref name="VDPVcurrent" /> frameless|center|alt=World map of polio cases in 2023 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- | Afghanistan||6||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Pakistan||6||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | DRC||0||106<br/>121||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}}<br/>{{color|#00f|cVDPV2}} |- | Nigeria||0||87||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Chad||0||55||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Guinea||0||47||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Madagascar||0||24||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Mali||0||16||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | CAR||0||14||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Kenya||0||8||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Yemen||0||8||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ivory Coast||0||6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Indonesia||0||6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Somalia||0||5||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Mozambique||0||4<br/>1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}}<br/>{{color|#00f|cVDPV2}} |- | Benin||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Tanzania||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Burkina Faso||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | South Sudan||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Niger||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Israel||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Mauritania||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Burundi||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Zambia||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Zimbabwe||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- class="sortbottom" | '''Total'''||12||530|| || |} {{stack end}} Twelve cases of WPV1 were reported in 2023, six in Afghanistan and Pakistan each. Additionally, 187 positive environmental samples were reported in those countries.<ref name="WPVcurrent" /> There were 391 confirmed cases of cVDPV2 reported to the WHO in 2023, across 22 countries, nineteen of which lie in Sub-Saharan Africa, with only a handful of cases in Indonesia, Yemen, and Israel being the exception. cVDPV1 was now concentrated in three countries, with 105 cases in the Democratic Republic of the Congo, 24 in Madagascar and four in Mozambique. No cVDPV3 virus had been detected for two years.<ref name="VDPVcurrent" />
The Independent Monitoring Board of the GPEI in its September 2023 Report<ref name=IMB>{{cite web | url=https://polioeradication.org/wp-content/uploads/2023/09/22nd-Report-of-The-Independent-Monitoring-Board-IMB.pdf | title=Closing in on zero}}</ref> mentioned a continued, geographically restricted, endemic transmission in the east of Afghanistan and in the southern districts of Pakistan's Khyber Pakhtunkhwa province. Only one wild polio genetic cluster remained in Afghanistan, with a much improved immunity rate (>90%) in the population. Levels of access in the country were the best they had been since 2018. However, a large pool of unvaccinated children remained in the Kandahar province, potentially leading to a large outbreak if the virus were to reappear there. In Pakistan, estimates were that the long-standing and intractable poliovirus circulation in most of the traditional endemic reservoirs had been eliminated. However, a positive environmental probe in Karachi, after no cases for over a year, raised concerns about the quality of the vaccination campaign in Pakistan. {{Clear}}
=== 2024 === {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+ Confirmed polio cases in 2024<ref name="WPVcurrent" /><ref name="VDPVcurrent" /> frameless|center|alt=World map of polio cases in 2024 |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- | Pakistan||74||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Afghanistan||25||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Yemen||0||187||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Nigeria||0||98||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ethiopia||0||44||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Chad||0||39||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | DRC||0||10<br/>15||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}}<br/>{{color|#00f|cVDPV2}} |- | Niger||0||16||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | South Sudan||0||10||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Angola||0||9||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Guinea||0||5<br/>4||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}}<br/>{{color|#80f|cVDPV3}} |- | Indonesia||0||7||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Somalia||0||7||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Cameroon||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Algeria||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Benin||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ivory Coast||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Liberia||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Mali||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Mozambique||0||1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Palestine||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Senegal||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Sudan||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- class="sortbottom" | '''Total'''||99||463|| || |} {{stack end}} During 2024 there were 99 reported cases of WPV1 with 74 from Pakistan and 25 from Afghanistan. Additionally, 649 positive environmental samples were collected in Pakistan and 124 in Afghanistan.<ref name="WPVcurrent" />
425 cases of cVDPV2 cases were found across twenty countries, all of which were in Sub-Saharan Africa except for Algeria in Northern Africa, Indonesia in Southeast Asia, and Yemen and Palestine in West Asia. In addition, seventeen countries had positive environmental samples of cVDPV2 but no confirmed cases: Bahrain, Djibouti, Egypt, Equatorial Guinea, Finland, Gambia, Germany, Ghana, Kenya, Mozambique, Poland, Senegal, Sierra Leone, Spain, Uganda, United Kingdom and Zimbabwe. France had one positive environmental sample of cVDPV3.<ref name="VDPVcurrent" />
Ten cVDPV1 cases were detected in the Democratic Republic of the Congo and one in Mozambique.<ref name="VDPVcurrent" />
After one and a half years without any cases, cVDPV3 reappeared with four new cases in Guinea between September and November.<ref name="VDPVcurrent" /> {{Clear}}
===2025=== {{stack begin| float=right}} {| class="wikitable sortable mw-collapsible mw-collapsed" style="font-size:85%"<!--Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL--> |+Confirmed polio cases in 2025<ref name="WPVcurrent"/><ref name="VDPVcurrent"/> frameless|center|alt=World map of polio cases in 2025 |- ! Country !! Wild<br/>cases !! Circulating<br/>vaccine-<br/>derived<br/>cases !! Transmission<br/>status !! Type |- | Pakistan||31||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Afghanistan||21||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Nigeria||0||66<br/>6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}}<br/>{{color|#80f|cVDPV3}} |- | Ethiopia||0||40||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Chad||0||31<br/>4||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}}<br/>{{color|#80f|cVDPV3}} |- | Yemen||0||30||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Angola||0||19||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Democratic Republic of the Congo||0||6<br/>5||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}}<br/>{{color|#80f|cVDPV1}} |- | Sudan||0||7||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Papua New Guinea||0||5||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Benin||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Niger||0||3||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Guinea||0||2||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV3}} |- | Somalia||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Central African Republic||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Burkina Faso||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Djibouti||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Cameroon||0||1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV3}} |- | Algeria||0||1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Laos||0||1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Mali||0||1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- class="sortbottom" | '''Total'''||52||233|| || |} {{stack end}} During 2025, there were 51 reported cases of WPV1 with 31 from Pakistan and 21 from Afghanistan. Additionally, 661 positive environmental samples were collected in Pakistan and 90 in Afghanistan, and, after 30 years of absence, three positive samples in Germany.<ref name="WPVcurrent"/>
217 cases of cVDPV2 were found across fourteen countries, all of which were in Sub-Saharan Africa with the exception of Yemen in West Asia and Papua New Guinea in Oceania. In addition, seven countries from Africa, three from Europe and two from West Asia had positive environmental samples of cVDPV2 but no confirmed cases: Algeria, Cameroon, Ivory Coast, Germany, Israel, Malawi, Namibia, Israel, Poland, Senegal, the United Kingdom, and Tanzania.<ref name="VDPVcurrent"/>
There has been one case each of cVDPV1 in the Democratic Republic of the Congo, Algeria, and Laos. Some environmental samples were detected this year in Djibouti and Israel with 10 cases each. Last virus was seen in July.<ref name="VDPVcurrent"/>
cVDPV3 continued in Nigeria (6), Chad (4), two in Guinea, and with one case in Cameroon. <ref name="VDPVcurrent"/>
{{Clear}}
===2026===
{{stack begin| float=right}} {| class="wikitable sortable mw-collapsible" style="font-size:85%"<!-Do not add a large margin here. This harms usability on mobile. Do not use {{small}} or <small> below: see MOS:SMALL-> |+ Confirmed polio cases in 2026<ref name="WPVcurrent" /><ref name="VDPVcurrent" /> |- ! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type |- | Afghanistan||4||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Pakistan||3||0||{{color|#f00|endemic}}||{{color|#f00|WPV1}} |- | Nigeria||0||24<br/>6||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}}<br/>{{color|#80f|cVDPV3}} |- | Democratic Republic of Congo||0||9||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Somalia||0||5||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Ethiopia||0||4||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Chad||0||4||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | South Sudan||0||3||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- | Togo||0||2||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Sudan||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Angola||0||1||{{color|#00f|cVDPV only}}||{{color|#00f|cVDPV2}} |- | Madagascar||0||1||{{color|#00f|cVDPV only}}||{{color|#80f|cVDPV1}} |- class="sortbottom" | '''Total'''||7||60|| || |} {{stack end}} {{As of|2026|5|25|post=,}} there have been one first case of WPV1 in Pakistan and three in Afghanistan so far. Positive environmental samples have also been collected in Pakistan (84) and in neighboring Afghanistan (34).<ref name="WPVcurrent" />
44 cases of cVDPV2 were found in Nigeria, the Democratic Republic of Congo, Somalia, Sudan, South Sudan, Angola, Chad, and Togo. Positive environmental samples were also reported in Algeria, Namibia, Malawi, the United Kingdom, and now even Australia.<ref name="VDPVcurrent" />
There have been six cases of cVDPV3 in Nigeria, and a few cases of cVDPV1 in South Sudan(3), Ethiopia(4), and Madagascar(1) so far.<ref name="VDPVcurrent" />
{{Clear}}
== See also == * {{Portal inline|Viruses}} * {{Portal inline|Medicine}} * Global Polio Eradication Initiative * ''The Final Inch'', a 2009 documentary film about the eradication effort * List of diseases eliminated from the United States * Mathematical modelling of infectious disease * Polio in Pakistan * Population health * 2024 Gaza Strip polio outbreak
{{clear}}
== References == {{Reflist}}
== Further reading == {{refbegin}} * {{cite journal | vauthors = Bigouette JP, Wilkinson AL, Tallis G, Burns CC, Wassilak SG, Vertefeuille JF | title = Progress Toward Polio Eradication - Worldwide, January 2019-June 2021 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 70 | issue = 34 | pages = 1129–1135 | date = August 2021 | pmid = 34437527 | pmc = 8389387 | doi = 10.15585/mmwr.mm7034a1 | doi-access = free }} {{refend}}
== External links == * {{cite web | url = https://polioeradication.org/polio-today/ | title = Polio today | work = Global Polio Eradication Initiative | date = 19 April 2024 | publisher = World Health Organization}}
{{Eradication of infectious disease}} {{PHEIC}}
Category:Infectious disease campaigns Category:Polio eradication Category:Public health emergencies of international concern Category:Vaccination