The efficacy of oral polio vaccine (OPV) was determired in infants immunized according to the currently recommended vaccination scheme in the city of S. Paulo. Trivalent OPV was administered to the infants at 8 week intervals, begining at 2 months of age, in well controled conditions at the Experimental Health Unit of the Escola Paulista de Medicina. The study showed that the administration of 2 doses of OPV resulted in poor seroresponses and was not sufficient for effective immunization of the infants to all three poliovirus types. Only the infant group which received a complete series of 3 vaccine doses exhibited an adequate level of immunity, as high as 75% of triple-immunes. The prevalence of antibodies to type 1, 2 and 3 polioviruses was 83%, 96% and 88%, respectively. If, however, the operational conditions observed in the health units of the city of S. Paulo and the low socio-economic level of the majority of the population are considered, it is expected that primary immunization based on 3 doses of OPV is inadequate in order to mantain the disease under effective control. It is advisable to increase the number of vaccine doses from three to five, in order to overcome the adverse effects upon routine OPV vaccination and assure a high level of immunity to poliomyelitis of our child population.
Poliomyelitis; Poliovirus vaccine, oral; Immunization