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Immune status of the population to poliovirus infection in Singapore.

A seroepidemiological survey conducted after two decades of mass immunization against poliomyelitis in Singapore showed a high level of herd immunity in the population to all three types of human poliovirus. Neutralizing antibodies to poliovirus 1, 2 and 3 were detected in 93.9-96.7% of the population between 6 months and over 40 years old. Adults above 30 years of age had a relatively high level of susceptibility to poliovirus infection, with 10.2-12% in the over-30-year age group possessing no neutralizing antibody against poliovirus 1, 14.3% in the 40+ age group against poliovirus 2, and 14% in the 30-39-year age group against poliovirus 3. The geometric mean titres showed a general decline among the older age groups. There were no statistically significant differences in the immune status by sex and by ethnic groups (Chinese, Malays and Indians). The importance of maintaining a high coverage of immunization, monitoring the herd immunity of the population to identify high-risk groups, and advising adults travelling to the endemic areas to be immunized against poliomyelitis was stressed.