Persistence of antibody following immunization of children with groups A and C meningococcal polysaccharide vaccines.

Persistence of antibody following immunization with groups A and C meningococcal polysaccharides was studied in two groups of children. Cohort 1 (20 children, 2 to 11 years of age) received two doses of A vaccine three years apart; cohort 2 (1,345 children, 6 to 8 years of age) received A or C vaccine initially and the heterologous vaccine one year later. No significant reactions were observed. Geometric mean anti-A concentrations one month after primary and booster immunization in cohort 1 were 8.77 and 13.08 microgram/ml, respectively. Mean anti-A concentration declined 32% one year after booster immunization, but then stabilized. Mean anti-A and anti-C concentrations in cohort 2 were 9.35 and 9.12 microgram/ml, respectively, one month after primary immunization. Mean anti-A concentration declined to 5.54 and 3.62 microgram/ml while anti-C levels fell to 2.35 and 1.47 microgram/ml one and four years after immunization. The proportion of children in cohort 2 with greater than or equal to 2.0 microgram/ml of anti-A and anti-C four years after immunization were 80% and 40%, respectively. An antibody concentration greater than or equal to 2.0 microgram/ml has been associated with protection against meningococcal disease. The results suggest that routine immunization of young infants with group A vaccine may result in long-lasting immunity. The usefulness of the presently available group C vaccine appears to be limited to the control of epidemics.