Figure 1. . Impaired immunogenicity of oral poliovirus vaccine in India.

Seroconversion rates for India are obtained from a report by John [194], which combines results from several trials of trivalent OPV performed in Vellore between 1969 and 1976. Immunogenicity data from the USA are obtained from a study by McBean et al. [195] in which three doses of trivalent OPV were administered to infants in Maryland at 2, 4 and 18 months of age. Seroprevalence estimates at 18 and 20 months of age are interpreted here as seroconversion.

OPV: Oral poliovirus vaccine; PV1: Type 1 poliovirus; PV2: Type 2 poliovirus; PV3: Type 3 poliovirus.