Beyond the Last Wild Poliovirus
Beyond the Last Wild Poliovirus
October 24: World Polio Day 2026
A historic achievement—and an unfinished task
The world is closer than ever to ending polio. Wild poliovirus type 2 (WPV2) was certified eradicated in 2015, and wild poliovirus type 3 (WPV3) in 2019. Today, wild poliovirus type 1 (WPV1) remains in Afghanistan and Pakistan. [1–3] These achievements demonstrate that eradication is possible.
But the final phase of eradication has revealed another challenge: variant poliovirus (cVDPVs). cVDPVs originate from weakened oral poliovirus vaccine (OPV) viruses. When population immunity is insufficient, a vaccine-derived virus can continue to circulate, evolve genetically and, under prolonged circulation, regain neurovirulence and transmissibility, causing paralysis and sustained transmission. [4,5]
The distinction between wild and vaccine-derived polioviruses is therefore biologically important, but it should not obscure the public-health objective: stopping sustained poliovirus transmission in every population.
Different origin, same public-health consequence
Wild polioviruses and cVDPVs have different evolutionary origins, but they can have remarkably similar public-health consequences. Both can spread primarily through the faecal–oral route, circulate silently, cause acute flaccid paralysis and death, cross borders, and require sensitive surveillance, high population immunity, and rapid outbreak response.
For a child who becomes paralyzed, the virus's origin—wild or vaccine-derived—does not change the clinical outcome. This is why the final definition of success should be broader than simply stopping the last wild poliovirus.
A permanently polio-free world must be a world in which sustained transmission of all polioviruses has been interrupted, and the conditions for re-emergence are effectively controlled.
Africa and the emerging cVDPV challenge
The current epidemiology makes Africa central to this final phase. Our analysis of Global Polio Eradication Initiative (GPEI) data from 1 January 2024 to 17 August 2026 found that eight of nine countries reporting cVDPV1 detections or outbreaks were in Africa. For cVDPV2, 34 of 46 affected countries were African, while five of six countries reporting cVDPV3 were African. Five of six countries with concurrent cVDPV1 and cVDPV2 transmission were African, and all five countries reporting concurrent cVDPV2 and cVDPV3 transmission were African.
These findings do not make cVDPV an “African problem.” Poliovirus crosses borders through population movement, migration, trade and humanitarian corridors. Recent WHO assessments have documented continued cross-border transmission, including multiple cVDPV importation events between countries and regions. [6,7]
Importantly, cVDPV is not confined to low- or middle-income settings. In 2022, genetically linked cVDPV2 was detected in wastewater in the United Kingdom, the United States and Israel, including a paralytic cVDPV2 case in an unvaccinated adult in New York. Canada also detected vaccine-derived poliovirus in two wastewater samples collected in Montréal in August 2022. In late 2024, cVDPV2 genetically linked to a Nigeria lineage was detected in wastewater in Spain, Poland, Germany, the United Kingdom and Finland. [12–14] These events demonstrate that even countries with high routine vaccination coverage can experience poliovirus importation or detection and therefore remain part of the global polio-eradication effort.
Africa is the principal current epidemiological front—but cVDPV is unquestionably a global problem.
History offers a warning
The history of poliovirus type 2 is especially instructive. WPV2 was last detected in 1999 and was subsequently certified eradicated. Yet cVDPV2 emerged and became the most prominent vaccine-derived poliovirus problem during the post-WPV2 eradication era. In northern Nigeria, a major cVDPV2 outbreak beginning in the mid-2000s produced hundreds of cases and involved multiple independent emergence events. One major lineage circulated for more than six years in an under-immunized population. [8,9] The experience of type 3 provides another warning. WPV3 was certified eradicated in 2019, yet cVDPV3 outbreaks have subsequently occurred, including in African countries. [3,6]
These experiences demonstrate an important principle for the final phase of eradication: Eliminating a wild poliovirus serotype does not automatically eliminate all epidemiological risk associated with that serotype. Wild-virus eradication and interruption of vaccine-derived transmission are related but distinct milestones.
A broader vision for eradication
The final phase of polio eradication therefore requires three interconnected goals:
Interrupt the remaining WPV1 transmission;
Interrupt cVDPV1, cVDPV2 and cVDPV3 transmission wherever it occurs; and
Maintain sufficiently high population immunity and surveillance capacity to prevent re-emergence.
The GPEI strategy recognizes cVDPV control as an essential component of the endgame. The current strategy extension also emphasizes the importance of interrupting cVDPV2 outbreaks while maintaining progress toward WPV1 eradication. [10] In the longer term, the global programme must also complete the transition away from the use of live oral poliovirus vaccines under appropriate safeguards, while maintaining strong routine immunization, surveillance and outbreak-response systems. [10,11] This means that the end of polio cannot be defined simply by the disappearance of the last wild poliovirus from a laboratory result. It must ultimately mean the interruption of sustained transmission and the maintenance of the biological and programmatic conditions necessary to keep poliovirus from returning.
A global challenge requiring global solidarity
Polio eradication is a global collective-action challenge. The countries facing the greatest transmission risks often also face conflict, displacement, humanitarian emergencies, weak routine immunization systems and difficult access to children.
At the same time, countries that have eliminated poliovirus transmission remain vulnerable to importation. The detection of cVDPV in countries across Africa, Asia, Europe, North America and the Middle East demonstrates the interconnected nature of the risk. [6,12–14] This is why polio eradication cannot be separated into “high-risk countries” and “safe countries.” The level of risk may differ, but the global eradication objective is shared. For donors and governments, investment in cVDPV control should therefore not be viewed as competing with WPV1 eradication. It is part of completing eradication.
Sustained financing is needed not only for emergency vaccination campaigns, but also for the less visible infrastructure on which eradication depends: routine immunization, environmental and acute flaccid paralysis surveillance, laboratory capacity, genomic analysis, vaccine supply, cross-border coordination, community engagement and rapid outbreak response.
A World Polio Day call for solidarity
World Polio Day 2026 should renew a simple commitment: A world without wild poliovirus but with continuing cVDPV transmission is not yet a polio-free world.
The final stage of eradication requires us to think beyond the last wild poliovirus. It requires the international community to interrupt WPV1 transmission, stop ongoing cVDPV transmission, maintain high population immunity, and prevent the re-emergence and international spread of poliovirus.
The goal should therefore be clear:
Eradicate WPV1. Interrupt cVDPV1, cVDPV2 and cVDPV3 transmission. Prevent re-emergence. Sustain a permanently polio-free world.
Sustained political commitment, predictable financing, high-quality surveillance, strong routine immunization, scientific innovation and global solidarity will remain essential until every form of sustained poliovirus transmission has been stopped.
We must not simply finish the fight against wild poliovirus. We must finish the fight against poliovirus.
References
World Health Organization (WHO). Poliomyelitis. WHO Questions and Answers. Updated 2025.
https://www.who.int/news-room/questions-and-answers/item/poliomyelitisGlobal Polio Eradication Initiative (GPEI). Global eradication of wild poliovirus type 2 declared. 2015.
https://polioeradication.org/news/global-eradication-of-wild-poliovirus-type-2-declared/Global Polio Eradication Initiative (GPEI). Two out of three wild poliovirus strains eradicated: global eradication of wild poliovirus type 3 declared. 24 October 2019.
https://polioeradication.org/news/two-out-of-three-wild-poliovirus-strains-eradicated/Bigouette JP, Wilkinson AL, Tallis G, Burns CC, Wassilak SGF, Vertefeuille JF. Progress Toward Polio Eradication—Worldwide, January 2019–June 2021. MMWR Morbidity and Mortality Weekly Report. 2021;70(34):1129–1135. doi:10.15585/mmwr.mm7034a1.
Mbaeyi C, Baig S, Khan Z, et al. Progress Toward Poliomyelitis Eradication—Pakistan, January 2020–July 2021. MMWR Morbidity and Mortality Weekly Report. 2021;70(39):1359–1364. doi:10.15585/mmwr.mm7039a1.
World Health Organization (WHO). Statement of the Forty-Fifth Meeting of the Polio IHR Emergency Committee. 25 August 2026.
https://www.who.int/news/item/25-08-2026-statement-of-the-forty-fifth-meeting-of-the-polio-ihr-emergency-committeeGlobal Polio Eradication Initiative (GPEI). Polio This Week: Country Updates. September 2026.
https://polioeradication.org/about-polio/polio-this-week/Wassilak SG, Pate MA, Wannemuehler K, et al. Outbreak of Type 2 Vaccine-Derived Poliovirus in Nigeria: Emergence and Widespread Circulation in an Underimmunized Population. The Journal of Infectious Diseases. 2011;203(7):898–909. doi:10.1093/infdis/jiq140.
Burns CC, Shaw J, Jorba J, et al. Multiple Independent Emergences of Type 2 Vaccine-Derived Polioviruses during a Large Outbreak in Northern Nigeria. Journal of Virology. 2013;87(9):4907–4922. doi:10.1128/JVI.02954-12.
Global Polio Eradication Initiative (GPEI). Polio Eradication Strategy 2022–2026: Delivering on a Promise—Strategy Extension to 2029. World Health Organization; 2025.
https://www.who.int/publications/i/item/9789240109506Global Commission for the Certification of Poliomyelitis Eradication (GCC). Report of the Twenty-Fourth Meeting of the Global Commission for Certification of Poliomyelitis Eradication. 2023/2024.
https://polioeradication.org/World Health Organization (WHO). Statement of the Thirty-Fourth Meeting of the Polio IHR Emergency Committee. 2 February 2023.
https://www.who.int/news/item/02-02-2023-statement-of-the-thirty-fourth-polio-ihr-emergency-committeeCenters for Disease Control and Prevention (CDC). Notes from the Field: Detection of Vaccine-Derived Poliovirus Type 2 in Wastewater—Five European Countries, September–December 2024. MMWR Morbidity and Mortality Weekly Report. 2025;74.
https://www.cdc.gov/mmwr/Public Health Agency of Canada (PHAC). Vaccine-derived poliovirus detected in wastewater samples in Montreal, Quebec. 23 December 2022.
https://www.canada.ca/en/public-health/news/2022/12/vaccine-derived-poliovirus-detected-in-wastewater-samples-in-montreal-quebec.html