Assessment of poliovirus antibody seroprevalence in high risk areas for vaccine derived poliovirus transmission in Madagascar

Background Vaccine-derived polioviruses (VDPV) outbreaks typically occur in areas of low poliovirus immunity. Madagascar successfully eradicated wild poliovirus in 1997; however, multiple VDPV outbreaks have occurred since then, and numerous vaccination campaigns have been carried out to control the VDPV outbreaks. We conducted a survey of poliovirus neutralizing antibodies among Malagasy children to assess performance of vaccination campaigns and estimate the risk of future VDPV outbreaks. Methods This was a random community survey in children aged 6-11 months, 36-59 months and 5-14 years of age in high risk areas of Madagascar (Mahajanga, Toliara, Antsalova, and Midongy-atsimo); and in a reference area (Antananarivo). After obtaining informed consent, basic demographic and vaccination history, 2 mL of peripheral blood were collected. Neutralizing antibodies against all three poliovirus serotypes were detected by using a standard microneutralization assay. Results There were 1500 children enrolled and 1496 (>99%) provided sufficient quantity of blood for analysis. Seroprevalence for poliovirus type 1 (PV1) was >90% in all age groups and study areas. PV2 seroprevalence ranged between 75-100%; it was lowest in the youngest age group in Midongy and Toliara. PV3 seroprevalence ranged between 79-100%. Seroprevalence in the reference area was not significantly different from polio high risk sites. Discussion Madagascar achieved high population immunity. In order to preserve these gains, routine immunization needs to be strengthened. Currently, the risk of new VDPV emergences in Madagascar appears low.