CONCISE COMMUNICATION Poliovirus Circulation among Schoolchildren during the Early Phase of the 1992–1993 Poliomyelitis Outbreak in The Netherlands

children at 7 schools for evidence of infection with the outbreak virus, poliovirus type 3 (PV3), to determine the extent of the outbreak and the protection of the herd immunity. Seventy-seven children (8.9%) showed evidence of recent wild-type PV3 infection, as determined by virus iso-lation and/or poliovirus type–specific IgM assay. Most infected children lived in the same area as the index case patient, attended an orthodox-reformed (OR) primary school, and had not been vaccinated. At the OR school, as many as 22 % of children immunized with inactive polio-virus vaccine were found to have evidence of recent infection, which is a significantly lower rate than that among unvaccinated children (59.5%). No evidence of vaccination was seen in 25.5%–43.1 % of children at OR schools. Seroprevalence of antibodies against the 3 types of poliovirus suggested that no poliovirus circulation had occurred between the 1978 and 1992– 1993 outbreaks. In the Netherlands, since 1957, inactivated poliovirus vaccine (IPV) has been administered to children at ages 3, 4, 5, and 11 months and 4 and 9 years. The vaccination coverage for 3 doses at age 1 year is 97%. Local outbreaks of polio occurred in th