FACTORS AFFECTING THE IMMUNOGENICITY OF ORAL POLIOVIRUS VACCINE - A PROSPECTIVE EVALUATION IN BRAZIL AND THE GAMBIA

To assess factors that may influence the immunogenicity of oral poliov irus vaccine (OPV), neutralizing antibody responses were measured in 1 409 infants in Brazil and the Gambia who were randomized to receive on e of four different formulations of OPV at similar to birth and at 6, 10, and 14 weeks. Overall seroconversion rates at the end of the trial were 85% for poliovirus type 1 (P1), 94% for type 2 (P2), and 68% for type 3 (P3). Factors associated with vaccine failure included high le vels of maternal antibody (P1, P2, and P3), vaccination during the rai ny season (P1, P2, and P3), diarrhea at the time of vaccination (P2 an d P3), household exposure to other OPV recipients (P1), and breast-fee ding (P3) (P < .05 for each factor, logistic regression analysis). OPV containing twice the standard potency of Sabin type 1 virus increased seroconversion rates to P1 by 8% in Brazil(P < .05) and 15% in the Ga mbia (P < .001). Suboptimal responses to OPV in developing countries a re determined by a complex array of factors related to the vaccine, ho st, and environment.