Serological response and poliovirus excretion following different combined oral and inactivated poliovirus vaccines immunization schedules

A controlled study was conducted in Karachi, Pakistan to compare humoral and mucosal immune responses against polioviruses in infants who received oral poliovirus vaccine (OPV) at birth and at 6, 10, and 14 weeks according to the Expanded Program on Immunization (EPI) with infants who received either three doses of inactivated poliovirus vaccine (IPV) at 6, 10, and 14 weeks together with OPV or one additional dose of IPV at 14 weeks together, with the last dose of OPV. A total of 1429 infants were enrolled; 24-week serum specimens were available for 898 infants (63%). They all received a challenge dose of OPV type 3 at 24 weeks of age. The addition of three doses of IPV to three doses of OPV induced a significantly higher percentage of seropositive children at 24 weeks of age for polio 1 (97% versus 89%, P<0.001) and polio 3 (98% versus 92%) compared to the EPI schedule. However, the one supplemental dose of IPV at 14 weeks did not increase the serological response at 24 weeks. Intestinal immunity against the challenge dose was similar in the three groups. Combined schedules of OPV and IPV in the form of diphtheria-pertussis-tetanus-IPV vaccine (DPT-IPV) may be useful to accelerate eradication of polio in developing countries.