Immunogenicity of Group A and Group C Meningococcal Polysaccharides in Human Infants

Ninety-two infants, 10 weeks to 21 months of age, received one to three sc injections of 12.5-100 µg of polysaccharide from group A (39 infants) or group C (53 infants) Neisseria meningitidis. No local or systemic side effects were observed. There was no clear dose-response relationship over the range of antigen concentrations administered. Three- and seven-month-old infants produced geometric mean concentrations of antibody of 0.49–1.29 µg/ml of serum within four weeks of primary immunization with group A or group C polysaccharide. These infants also had significantly elevated concentrations of antibody at seven and 18 months of age as compared with nonimmunized infants. Eighteen-month-old infants produced geometric mean concentrations of antibody of 4.69 µg/ml and 3.11 μg/ml of serum within four weeks of primary immunization with group A or Group C polysaccharide, respectively. The antibody response to booster injections of the group C antigen did not differ from that induced by primary immunization. However, the difference between means of the antibody response of 18-month-old infants to primary and secondary injections of the group A antigen (4.69 µg/ml vs. 9.10 µg/ml) approached significance. Simultaneous administration of the group A and group C vaccines in separate syringes to seven- or 18-month-old infants did not alter the antibody response to either antigen.