Circulation of Poliovirus during the Poliomyelitis Outbreak in the Netherlands in 1992-1993

A population-based study on the circulation of epidemic poliovirus during 1992-1993 outbreak in the Netherlands was carried out in order to assess whether the virus circulated outside the group of people who reject vaccinations on religious grounds and outside the area where these groups form sociodemographically closely knit network. The prevalence of poliovirus excretion was estimated in a cross-sectional study with a random sample of 2,400 children aged 5-14 years and 3,000 adults age 40-64 years; the sample was drawn from the municipal population registers in four regions (three inside and one outside the risk area). Fecal samples of virus isolation and characterization were submitted by mail, and a questionnaire was completed with age, sex, type and level of education, vaccination history, and religious denomination. Both a completed questionnaire and a fecal sample were received from 3,182 persons (response, 58.9%). Wild poliovirus was isolated only from children within the risk group and in the area at risk. The crude excretion rate of the epidemic poliovirus type 3 per 1,000 persons was 2.5, but it amounted to 70.7 for those belonging to Orthodox Reformed churches. The prevalence of vaccine virus excretion per 1,000 persons was 10.2 for children and 5.2 for adults. It was concluded that, during the 1992-1993 outbreak, the risk of poliovirus was restricted to religious subpopulations rejecting vaccination. The lack of evidence of poliovirus circulation outside these groups at risk supports the hypothesis that herd immunity is sufficiently maintained in a population vaccinated with inactivated polio vaccine.