COMBINED IMMUNIZATION OF INFANTS WITH ORAL AND INACTIVATED POLIOVIRUSVACCINES - RESULTS OF A RANDOMIZED TRIAL IN THE GAMBIA, OMAN, AND THAILAND

To assess an immunization schedule combining oral (OPV) and inactivate d poliovirus vaccines (IPV), a clinical trial was conducted in The Gam bia, Oman, and Thailand. Children were randomized to receive OPV at bi rth and at 6, 10, and 14 weeks of age; OPV at birth followed by both O PV and IPV at 6, 10, and 14 weeks of age; or placebo at birth followed by IPV at 6, 10, and 14 weeks of age. Serum specimens were available at 24 weeks for 1291 (77%) of 1685 enrolled infants. In the combined-s chedule group, the proportion of children seropositive at 24 weeks was 95%-99% for type 1, 99%-100% for type 2, and 97%-100% for type 3. In The Gambia and Oman, the combined schedule performed significantly bet ter than OPV for type 1 (95%-97% vs. 88%-90%) and type 3 (97%-99% vs. 72%-73%). Across the study sites, IPV given at 6, 10, and 14 weeks of age provided inadequate protection against poliovirus. The combined sc hedule provided the highest levels of serum antibody response, with mu cosal immunity equivalent to that produced by OPV alone.