Poliovirus antibodies in age groups: an assessment of obligatory vaccination in Belgium.

Since 1967, compulsory oral vaccination before 2 years of age has been nearly the only form of poliovaccination practiced in Belgium, and there have been almost no cases of polio. In recent sera from 2,225 Belgians, 2 year olds lacked demonstrable seroneutralizing antibody, in 31% for type 1, in 8% for type 2, and in 21% for type 3. The lack of antibodies grew as the children reached 11--12 years, at which age 65% lacked antibody for type 1, 15% for type 2, and 54% for type 3; only 19% had antibodies against all types. It is argued that this decline of antibodies is not due to insufficient vaccination in former years, but is a strong example of the waning of vaccine-acquired serum antibody. Antibody rates went up after age 12. The highest rates of types 1 and 3 antibodies were seen at age 20--59. There was some decrease of antibody after 60 years. Mean antibody titers paralleled positivity rates. Results of two laboratories studying different populations with different standard techniques were similar. The data support revaccination at school entrance.