Imported Wild-Type Poliovirus in Germany: A Modelling Study of Outbreak Potential

<title>Abstract</title> <p>Background In October 2025, wild poliovirus type 1 (WPV1) was detected in two wastewater samples in Hamburg. This is the first detection in Germany since 1992. Objective We aimed to estimate the probability of polio-associated acute flaccid paralysis (AFP) in Germany following imported WPV1 infections. Methods We developed a stochastic, age-stratified compartmental model for WPV1. To calibrate population immunity levels, we integrated national routine childhood immunization data with routine polio neutralization assay data from two German diagnostic laboratories. As a reference scenario, we modeled the arrival of an unvaccinated, WPV1-infected child aged 0-4 years. We estimated the impact of reduced national immunity and of communities with low immunization rates on AFP cases. Results In the reference scenario, our model predicted a very low probability that any AFP case occurs under current immunity levels (0.7%; 95% prediction interval PI 0.4-1.1%). The predicted median time-to-extinction of all WPV1 transmission following importation was 24 days (IQR 8-73 days), and endemic transmission (defined as sustained transmission in Germany for 365 days or longer) was unlikely (0.8%; 95%PI 0.5-1.2%). The probability of AFP cases increases substantially if overall immunization coverage declines, and particularly if WPV1 is imported into an under-immunized subpopulation. Conclusion Our findings suggest that current immunization levels in Germany make AFP cases and sustained WPV1 transmission unlikely. However, maintaining high routine immunization levels remains important to prevent resurgence of WPV1. To further reduce vulnerability, public health efforts should focus on closing polio immunization gaps, particularly in vaccine-hesitant communities.</p>