Immune Response of Human Infants to Polysaccharide Vaccines of Groups A and C Neisseria meningitidis

Abstract

Immunization of infants three to 24 months of age with polysaccharide vaccines derived from groups A and C Neisseria meningitidis induced no significant local or systemic adverse reactions. The antibody responses varied with age of the infant, quantity of vaccine, number of doses, molecular size of the vaccine polysaccharide, and the degree of preexisting, naturally acquired immunity to N. meningitidis. No response to group A vaccine was detected in three-month-old infants, but most seven- and 12-month-old infants responded to primary immunization, achieving geometric mean concentrations of antibody protein (measured as antibody to group A polysaccharide) of 0.39 and 0.84 ,µg/ml, respectively. Significant anamnestic responses were seen at seven and 12 months of age but not at 24 months. Primary immunization with group C vaccine elicited a response in 90% of three-month-old and in 100% of seven- and 12-month-old infants. The 100-µg dose of vaccine induced geometric mean concentrations of antibody to group C polysaccharide of 0.49, 1.41, and 2.62 ,µg/ml, at three, seven, and 12 months of age, respectively. These values were larger than those achieved with smaller doses. No anamnestic responses were observed with the group C vaccine. Booster injections resulted in lower concentrations of antibody to group C polysaccharide at seven and 12 months of age than did primary immunization, except after two booster doses of 10 µg. This depressed response to booster immunization was not observed in two-year-old children.