Wastewater poliovirus detections in Europe may reflect seasonal infection patterns rather than consistent importation

Presented by

Dr Kimberley Hansford , Sciensano, Belgium

Conference

ESCMID Vaccines

Poliovirus was detected in sewage samples in 2024 in multiple European countries, including Germany, Spain, Finland, Poland, and the UK [1]. Genetic analyses of the vaccine-derived poliovirus 2 (NIE-ZAS-1) indicated at least 1 year of circulation and were initially interpreted as evidence of multiple simultaneous importations [2]. At ESCMID Vaccines 2025, Dr Kimberley Hansford (Sciensano, Belgium) presented an alternative interpretation, based on poliovirus seasonality [3].

The analysis simulated hypothetical wastewater detection curves using poliovirus case counts from Belgium between 1940 to 1965, incorporating polio seasonality and faecal shedding patterns. A summer onset assumption was applied, and the final curves were adjusted using local climate data for European cities with poliovirus detections to determine the start of the summer season.

Real-world detected wastewater poliovirus load for all 36 European cities with detections fell within the intervals predicted by the model. “This gives us the indication that polio could have been imported at a low level of circulation in those areas”, said Dr Hansford. “What we saw with the sudden onset of wastewater detections was a natural seasonal peak occurring as transmission increased in those areas.”

Overall, NIE-ZAS-1 wastewater detections in late 2024 were consistent with silent, endemic circulation characterised by seasonal amplification, rather than with multiple simultaneous importations. “My conclusion is that when we talk about vaccines, let’s not forget polio”, said Dr Hansford. “It remains very important, and it is something we need to remember.”

Detections of poliovirus in sewage samples require enhanced routine and catch-up vaccination and increased surveillance. Available from: https://www.ecdc.europa.eu/en/news-events/detections-poliovirus-sewage-samples-require-enhanced-vaccination-surveillance (accessed 15 September 2025)
Rowland T, et al. Euro Surveill. 2025;30(16):2500025.
Hansford K, et al. Seasonal amplification of poliovirus detection in Europe: An evidence may suggest silent circulation of the NIE-ZAS-1 cVDPV2 variant. 6^th ESCMID Conference on Vaccines, 10–13 September 2025, Lisbon, Portugal.

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