Absence of wild poliovirus circulation among healthy children in a rural area with high oral poliovirus vaccination coverage.

Poliovirus circulation in a rural community was studied by a stool sample survey. No acute paralytic poliomyelitis case had been reported from the study area during the previous 5 months. Immunization coverage in age groups 7 to 12 months and 12 to 60 months was 95.8 and 94 per cent, respectively. Of the 257 children from whom stool samples were collected (about 6% of the child population), 161 (62.6%) were positive for virus isolation. Poliovirus was isolated from 60 (23.3%) children. All three poliovirus types were detected (41 type 1, 16 type 2 and 3 type 3). Intratypic differentiation tests classified these isolates as vaccine-like. Among the children excreting poliovirus, the proportion of those who did not receive polio vaccine within 30 days prior to the sample collection was 46.3, and 68.7 per cent for poliovirus type 1 and 2, respectively. It was concluded that these poliovirus excreting children were infected by the vaccine strains circulating in the environment. The survey showed that wild poliovirus was not detectable within five months after the last case of acute poliomyelitis. Displacement of the wild virus from the environment and circulation of vaccine virus was achieved by high vaccination coverage in this area.