Serum antibodies to capsular polysaccharide vaccine of group A Neissera meningitidis followed for three years in infants and children.

The persistence of antibodies to the capsular polysaccharide of group A Neissera meningitidis was studied in 2,030 persons vaccinated at the age of 10 weeks to 19 years and followed for three years. Both the initial antibody response and the persistence of elevated serum titers of antibody were markedly age-dependent. In infants younger than 12 months, a statistically significant antibody response was obtained after a booster dose of vaccine and was maintained for one year. In infants aged 12-17 months, the response after booster vaccination was higher and was maintained for two years. Children older than 17 months did not receive a booster injection. The initial response in the age group 18-23 months was good, but the decline of antibody level was more rapid, so that an elevated antibody titer was not maintained for more than one year. With increasing age, the decrease of the vaccination-induced antibody levels was progressively slower throughout the age bracket studied.