Efficacy of inactivated poliovirus vaccine in India.

The immunogenic efficacy of inactivated (Salk) poliovirus vaccine (IPV) was evaluated in infants in India, in view of the high frequency of vaccine failure after immunization with oral (Sabin) poliovirus vaccine (OPV). A total of 150 infants, aged 6-45 weeks, were given 3 doses of IPV, with intervals of 4 or 8 weeks between doses. The effect on the antibody response of child's age, presence of maternal antibody before immunization, and interval between doses was assessed. The overall seroconversion rates to poliovirus types 1, 2, and 3 were 99%, 89%, and 91%, respectively. Seroconversion rates to types 2 and 3, and antibody titres to types 1 and 2, were higher (i) in infants given vaccine doses at 8-week intervals and (ii) in those without detectable maternal antibody. The seroconversion rates in infants without maternal antibody, who were given IPV at 8-week intervals, were 100%, 100%, and 96.2% to poliovirus types 1, 2, and 3, respectively. Thus the immunogenic efficacy of IPV was found to be satisfactory.