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, eventhough 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.