Antibody response of children immunized with poliovaccines: an evaluation using two strains of poliovirus type 1.

Neutralizing antibody response of children immunized with either OPV (3 doses), or IPV (2 doses) was evaluated against poliovirus type 1 Sabin vaccine strain and a local neurovirulent isolate. Both vaccines elicited significantly better antibody response against the vaccine strain than against the neurovirulent isolate. Moreover, approximately 35 per cent of sera contained very low levels of antibody against the virulent virus in spite of good antibody titre against the vaccine strain. The observed difference in antibody response to the wild and the vaccine strains was significant. The differential immune response could be one of the reasons of paralytic disease observed even after administration of OPV (3), in some children if infecting virus dose is high, as in case of urban slums in endemic areas.

Intratypic characterization of poliovirus type 1 isolates.

Intratypic serodifferentiation of 607 strains of poliovirus type 1 isolated from diverse epidemiological groups, was carried out using strain-specific antisera and monoclonal antibodies. The isolates were from patients of paralytic poliomyelitis from Marathwada (an epidemic area) and Bombay (endemic area) and from healthy children from Emmaneshwaram (vaccinated area). From Marathwada where mass scale vaccination with oral poliovirus vaccine (OPV) was performed to contain the spread of the epidemic, non-vaccine-like and vaccine-like virus strains were isolated. Only non-vaccine-like virus strains were detected among the Bombay isolates. In Emmaneshwaram mass-scale vaccination performed in 1986 had earlier led to the replacement of the wild poliovirus with the vaccine strains. However, even though systematic OPV immunization reached 93 per cent coverage in 1987 and 1988, majority of isolates from Emmaneshwaram were found to be non-vaccine-like. Results showed that routine immunization of children with OPV was not sufficient to displace the wild virus. A small number of antigenic variants were detected. The frequency of such variants was more when mass-scale vaccinations were performed after paralytic poliomyelitis outbreaks. Using a panel of monoclonal antibodies epitope mapping of these variants was performed.

Efficacy of three doses of oral polio immunization beginning within the first four days of life.

A study was carried out to test the efficacy of oral polio immunization commencing in the newborn period. In Group A, 47 term newborn infants were given trivalent oral polio vaccine (TOPV) within the first four days, at one month and at two months. In Group B, 21 infants were given TOPV at 3, 4 and 5 months. The seroconversion rates for types 1, 2 and 3 were 87.2, 95.7 and 72.3%, respectively in Group A and 85.7, 95.2 and 66.7%, respectively in Group B after 3 doses of TOPV, the differences being insignificant. Oral polio immunization beginning in the newborn period was as effective as when commenced at 3 months of age. Before immunization, the number of babies with protective titers against polioviruses were significantly more in Group A as compared to Group B. Thus, the later onset of immunization schedule leaves more children susceptible to poliomyelitis during the first 3 months of life.