Vaccine-Derived Poliovirus in European Wastewater, 2024

Summary

• Known before: a vaccine-derived poliovirus type 2 (VDPV2) lineage from Nigeria had been detected in 21 other countries in Africa.
• New here: in the weeks ending September 22 to December 22, 2024, VDPVs genetically linked to that lineage turned up in wastewater in 16 cities in five European countries. No human polio cases or infections were reported with them.
• What it means: the detections look like importations of the virus. While VDPV2 keeps circulating in Africa, more importations — and spread among under-vaccinated people outside Africa — are possible. High polio vaccine coverage is critical to prevent disease and stop the virus taking hold.

European cities with variant poliovirus type 2 detected in wastewater. CDC.

Background

Poliovirus is highly contagious. It can cause a flu-like illness and, rarely, acute flaccid paralysis (AFP); since 1988 every country has aimed to eradicate it.

• Vaccine-derived polioviruses (VDPVs) are rare disease-causing strains that can arise when the oral polio vaccine strain mutates during long circulation in under-immunized populations.
• The WHO European Region has been free of endemic polio since 2002, but imported VDPVs can start local circulation (cVDPV) in under-vaccinated communities. Type 2 cVDPV circulated in the United Kingdom in 2022, linked to spread in Israel, the United States and Canada.
• Because most polio infections cause no symptoms and the virus is shed in stool, many European countries add environmental surveillance — systematic wastewater sampling — to their AFP and enterovirus surveillance.

The detections

All five countries — Spain, Poland, Germany, the United Kingdom and Finland — have high national coverage with inactivated poliovirus vaccine (IPV).

• First: wastewater from the Barcelona metropolitan area, week of September 16–22, 2024.
• Then, weeks ending October 27 to December 22: sites in Poland (two), Germany (nine), the United Kingdom (four) and Finland (one).
• Source: sequencing linked them to the cVDPV2 NIE-ZAS-1 emergence, first found in Zamfara, Nigeria, in July 2020 and still circulating there in 2024. It has caused polio outbreaks in 15 other North and West African countries and been found in wastewater in six more African countries.

Weeks with VDPV2 found, by site (weeks ending, 2024; data reported to WHO as of January 24, 2025):

One detection is one week with poliovirus found at a site.

What the genes show

• The European isolates differ from the Sabin 2 vaccine strain by 43–50 nucleotides in the VP1 capsid region; 38 of those differences are shared by all of them.
• Together they differ by 13 nucleotides from the closest known NIE-ZAS-1 isolates, found in Algeria, Guinea and Mali — so they form a single lineage, more closely related to each other than to any non-European isolate.
• Even so, they vary: isolates found at the same time at different sites in the same country were substantially different.

No human polio cases or symptomless infections were reported with any of them.

Preliminary conclusions

• Circulating polioviruses gain about one nucleotide change a month, so the shared 13-nucleotide difference suggests about a year of undetected circulation outside the areas Europe's wastewater network covers.
• So far — given the diversity of isolates in the same area and how rarely closely related virus was found twice at one site — the importations don't seem to have caused much person-to-person spread.
• The affected countries are vaccinating targeted groups with IPV to close immunity gaps, and have stepped up AFP and wastewater surveillance.

The event shows the continuing worldwide risk from circulating VDPVs and the need to eradicate all polioviruses. Wastewater surveillance is a useful addition to high-quality AFP surveillance for spotting importations, and high vaccine coverage in every population group remains critical.

Sources

Based on "Notes from the Field: Detection of Vaccine-Derived Poliovirus Type 2 in Wastewater — Five European Countries, September–December 2024," by Shahin Huseynov, Eugene Saxentoff, Sabine Diedrich, Javier Martin, Magdalena Wieczorek, Maria Cabrerizo, Soile Blomqvist, Jaume Jorba and José Hagan, Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention; in the public domain, as MMWR declares for everything it publishes. See also the Eurosurveillance report on the same detections.