London, United Kingdom / New York, United States · 14 September 2022 — The World Health Organization confirmed that circulating vaccine-derived poliovirus type 2 (cVDPV2) had been detected in environmental surveillance samples from both the United Kingdom and the United States, triggering national public health emergencies in two countries that had long been considered polio-free.
The detections, reported in a WHO Disease Outbreak News on 14 September 2022, revealed a genetically linked chain of transmission spanning at least three countries. Genomic sequencing confirmed that viruses found in wastewater from New York State, London, and Jerusalem, Israel, were linked — evidence of international spread through communities with sub-optimal vaccination coverage.
London: From Surveillance to National Incident
Since February 2022, the WHO Global Polio Laboratory Network, based at the National Institute for Biological Standards and Control (NIBSC) in London, had been consistently detecting Sabin-like type 2 poliovirus isolates in sewage samples collected from the Beckton Sewage Treatment Works in London. Samples collected on 24 and 31 May showed sufficient mutations to qualify as vaccine-derived poliovirus type 2 (VDPV2).
Due to continued detection more than two months later, these samples were reclassified as "circulating" VDPV2 on 8 August 2022 — a designation that indicates evidence of community transmission rather than isolated importation.
The UK Health Security Agency (UKHSA) declared a national incident. In response, the Joint Committee on Vaccination and Immunisation (JCVI) recommended a supplementary inactivated polio vaccine (IPV) booster campaign targeting all children aged 1–9 years across London, launched in August 2022. A catch-up campaign for children under 5 had already been implemented in June.
No human cases of polio were reported in the United Kingdom during the incident. The last detection of the virus in London sewage linked to this event occurred in November 2022, and WHO removed the UK from the list of "infected" countries in December 2023.
New York: The First US Paralytic Case in Nearly a Decade
Between 21 April and 26 August 2022, Sabin-like type 2 poliovirus was consistently detected in environmental samples from Rockland County, New York, and surrounding counties. In late July, a case of VDPV2 was confirmed in an unvaccinated individual in Rockland County who presented with paralysis. The individual had no recent history of international travel.
Following the clinical case and wastewater detections, health authorities expanded surveillance and launched aggressive vaccination campaigns targeting under-vaccinated communities. On 9 September 2022, New York State declared a disaster emergency due to polio, allowing pharmacists and additional health professionals to administer polio vaccine and enabling standing orders for vaccinations.
Understanding Vaccine-Derived Poliovirus
Vaccine-derived poliovirus is a well-documented phenomenon. The oral polio vaccine (OPV) contains a live, weakened form of poliovirus. On rare occasions, when replicating in the gastrointestinal tract, OPV strains genetically change and may spread in communities that are not fully vaccinated. The lower the population immunity, the longer the virus survives and the more genetic changes it undergoes. In very rare instances, the vaccine-derived virus can genetically change into a form that can cause paralysis.
The detection of VDPV in at least two different sources, at least two months apart, that are genetically linked and showing evidence of community transmission, triggers classification as "circulating" vaccine-derived poliovirus.
| Location | First Detection | Classification Date | Human Cases | Key Response |
|---|---|---|---|---|
| London, UK | February 2022 | 8 August 2022 | None | IPV booster campaign for children 1–9 |
| New York, USA | April 2022 | August 2022 | 1 (paralytic) | State disaster emergency, vaccination campaigns |
| Jerusalem, Israel | January 2022 | — | Under investigation | Enhanced surveillance |
Vaccination Coverage Gaps
According to WHO/UNICEF estimates, vaccine coverage for three routine doses of polio vaccine in children aged 12 months was 93% in the United Kingdom and 92% in the United States in 2021 — below the 95% threshold WHO recommends at the district level to prevent community transmission.
The Global Eradication Context
The detections in London and New York served as a stark reminder that until polio is globally eradicated, polio-free countries remain at risk of re-infection. The Global Polio Eradication Initiative (GPEI) has been working since 1988 to eliminate the disease, but wild poliovirus remains endemic in Afghanistan and Pakistan, and cVDPV2 outbreaks continue to affect multiple regions.
WHO reiterated to all Member States the importance of:
- Maintaining polio vaccination coverage above 95% in every district or municipality
- Maintaining high-quality surveillance for acute flaccid paralysis (AFP)
- Optimising environmental and enterovirus surveillance
- Updating national poliovirus outbreak response plans for rapid detection and response
The events of 2022 demonstrated that wastewater surveillance — long used in polio-endemic countries — is a critical tool even in nations that have eliminated the disease. Environmental monitoring provided the early warning that clinical surveillance alone could not, allowing authorities to act before widespread transmission could occur.
Sources
- World Health Organization, "Detection of circulating vaccine derived polio virus 2 (cVDPV2) in environmental samples — the United Kingdom and the United States of America," Disease Outbreak News, 14 September 2022.
- UK Health Security Agency, "Environmental surveillance for polio,"
- US CDC, "Public Health Response to a Case of Paralytic Poliomyelitis in an Unvaccinated Person and Detection of Poliovirus in Wastewater — New York, June–August 2022," MMWR 71:1065–1068.
- US CDC, "United States confirmed as country with circulating vaccine-derived poliovirus," 13 September 2022.
- Global Polio Eradication Initiative.
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Institutional Research Desk · Foresight Institute of Research and Translation
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