SERORESPONSE TO TRIVALENT ORAL POLIOVIRUS VACCINE AS A FUNCTION OF DOSAGE INTERVAL

Seroresponses to trivalent oral poliovirus vaccine are not uniform thr oughout the world. Definition of the variables that determine successf ul immunization is vital to ensure global polio eradication. One such variable may be dosage interval. To investigate this effect 108 infant s were enrolled in a clinical trial and randomly assigned to receive t hree doses of trivalent oral poliovirus vaccine (standard United State s formulation) at 2, 3 and 4 or 2, 4 and 6 months of age. After three doses of vaccine given before 6 months of age, immunity was virtually complete for each of the three poliovirus types in both groups. After two doses the seroresponse rate to each type was less with the shorter dose interval. However the difference was not significant (P = 0.15) in the sample size studied. Such responses differ markedly from those seen in developing countries, where four or more doses of vaccine may fail to provide complete protection. Differences other than dosage int erval must contribute to those failures.