Long-term persistence of poliovirus neutralizing antibodies in the era of polio elimination: An Italian retrospective cohort study

INTRODUCTION: The extensive use of oral and inactivated poliovirus (PV) vaccines has driven progress toward the global eradication of wild PV2 and PV3 and the elimination of PV1 in most countries, including Italy. Although the persistence of circulating neutralizing antibodies among the vaccinated is unclear, it is estimated that > 99% of the population vaccinated according to the recommended protocol should be protected for at least 18 years. METHODS: This study evaluated the seroprevalence of anti-PV neutralizing antibodies and the long-term immunogenicity of the oral poliovirus vaccine (OPV) in a sample of medical students and residents of the University of Bari who attended the Hygiene Department for a biological risk assessment between April 2014 and October 2020. RESULTS: The prevalence of protected vaccinated individuals was > 90% for PV1, PV2, and PV3. Specifically, >99% of the study group was protected against PV1, > 98% against PV2, and almost 93% against PV3. Protective antibodies against all three viruses persisted for at least up to 18 years after administration of the last OPV dose, with PV1 and PV2 antibodies detected in > 95% of the participants > 30 years after the last OPV dose. CONCLUSIONS: The childhood series of four doses of OPV guarantees a long duration of protection, despite the elimination of the virus and therefore the absence of a natural booster. However, until PV1 is completely eradicated, maximum vigilance on the part of public health institutions must be maintained.