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Investigations and Outcomes

The first European detection of VDPV2 was in wastewater sampled in the Barcelona, Spain metropolitan area during the week of September 16–22, 2024. During weeks ending October 27–December 22, 2024, ES samples from 16 total additional sites in metropolitan areas of Poland (two sites), Germany (nine), the United Kingdom (four) and Finland (one) tested positive for related polioviruses (Table). Genetic sequence analysis confirmed that these detections were linked (1) to the cVDPV2 NIE-ZAS-1 emergence^§ that was first detected in Zamfara, Nigeria in July 2020 (2), and which continues to circulate in Nigeria in 2024. Spread of cVDPV2 from this emergence group has caused outbreaks of poliomyelitis in 15 other countries in North and West Africa (WHO, unpublished data, 2024) and has been detected by ES in an additional six countries on the African continent (3). This activity was reviewed by obÌåÓý, deemed not research, and was conducted consistent with applicable federal law and obÌåÓý policy.^¶

Sequencing of the European cVDPV2 isolates identified a divergence in the VP1 capsid protein coding region of 43–50 nucleotides from the Sabin 2 vaccine strain. Overall, 38 of these nucleotide differences were found in all European isolates; they have a common divergence of 13 nucleotide changes from the closest known NIE-ZAS-1 isolates, which were previously detected in Algeria, Guinea, and Mali. The group of viruses detected in these European countries represents a single lineage (i.e., they exhibit a common pattern of nucleotide changes that make them more closely related to each other than to any other non-European isolates from the NIE-ZAS-1 emergence); however, there is a range of genetic differences within the cluster, and contemporaneous isolations from different sites in the same country exhibited substantial divergence from one another (4).

Importantly, no human polio cases or asymptomatic infections were reported in association with detection of this group of viruses.

Preliminary Conclusions and Actions

Since circulating polioviruses are known to accumulate mutations at an average of about one nucleotide change per month, (5) the common 13-nucleotide difference from the parent cluster suggests approximately 1 year of undetected circulation outside the catchment areas of the European ES network before this detection event. To date, the data (i.e., the diversity of isolates within the same geographic area and the paucity of repeated isolations of closely related virus from a single site) suggest that these importations have not resulted in substantial person-to-person transmission. The affected countries are actively working to prevent establishment of local transmission by vaccinating targeted populations with IPV to close immunity gaps and they have intensified AFP surveillance and ES for poliovirus. This event highlights the ongoing risk from circulating VDPVs worldwide and the need for intensified global efforts to eradicate all polioviruses. Wastewater surveillance is a useful supplement to high quality AFP surveillance to detect importation and monitor potential population risk. High coverage with poliovirus vaccine across all population groups is critical to protecting against AFP and other forms of polio disease and preventing establishment of local circulation following poliovirus importation.