IMMUNOGENICITY OF A SUPPLEMENTAL DOSE OF ORAL VERSUS INACTIVATED POLIOVIRUS VACCINE

In many developing countries, the immunogenicity of three doses of liv e, attenuated, oral poliovirus vaccine (OPV) is lower than that in ind ustrialised countries. We evaluated serum neutralising antibody respon ses in 368 children aged 6 months and 346 children aged 9 months in Co te d'Ivoire who had previously received three doses of OPV at 2,3, and 4 months of age, and who were then randomised to receive a supplement al dose of OPV or enhanced-potency inactivated poliovirus vaccine (IPV ) at the time of measles vaccination. Although both vaccines increased seroconversion to all three poliovirus types, antibody responses were greater in the IPV group. Among children with no detectable antibody at baseline, IPV was 2 to 14 times more likely than OPV to induce sero conversion (type 1, 80% vs 40% at 6 months [p < 0.001] and 81%vs 14% a t 9 months [p < 0.001]; type 3, 76% vs 22% at 6 months [p < 0.001], an d 67% vs 5% at 9 months [p < 0.001]). Among children with detectable a ntibody at baseline, IPV was 1-4 to 7 times more likely than OPV to el icit 4-fold or more rises in antibody titre (p < 0.01). Geometric mean titres (GMTs) to all three poliovirus types were also consistently hi gher among IPV recipients than in OPV recipients when measured 4-6 wee ks and 13-17 months after vaccination. Administration of a supplementa l dose of IPV or OPV, which requires no additional visits or changes i n the existing immunisation schedule, might improve protection against paralytic poliomyelitis in communities with suboptimum seroconversion rates after three doses of OPV.