Cross-sectional Serologic Assessment of Immunity to Poliovirus in Differential Risk Areas of India: India Seroprevalence Survey - 2014.

OBJECTIVE: To assess the seroprevalence against all three poliovirus serotypes in traditional high risk areas in Bihar, lowest routine immunization coverage areas in Madhya Pradesh and migrant population living in Mumbai urban slums.

DESIGN: Cross-sectional Survey.

SETTING: Subjects selected by house to house visit (community based) and transported to government health facilities for further study procedures.

PARTICIPANTS: 1137 randomly selected healthy infants 6-11 months of age residing in the selected high-risk areas.

METHODS: Serum samples from the study site were shipped to Enterovirus Research Centre (ERC), Mumbai to determine the neutralizing antibodies against all three poliovirus serotypes. Children with a reciprocal antibody titer ≥1:8 were considered seropositive to the specific poliovirus.

RESULTS: Overall, seroprevalence in all the three study areas was 98%, 98% and 91% against poliovirus type-1, type-2 and type-3, respectively. Bihar had a seroprevalence of 99%, 99% and 92% against type-1, type-2 and type-3 respectively. Corresponding figures for Madhya Pradesh and Mumbai were 98%, 99% and 88% and 98%, 97% and 94%, respectively.

CONCLUSION: The study found high seroprevalence against all three poliovirus types not only in the traditional high-risk areas for polio in India, but even in the areas known to have low routine immunization coverage and among the migratory clusters living in Mumbai urban slums. Type-2 seroprevalence was found to be high. These findings are reassuring against the threat of emergence of circulating vaccine derived polioviruses (cVDPVs) in the country subsequent to switch from trivalent oral polio vaccine to bivalent oral polio vaccine in the routine immunization schedule from April 2016.