Abstract
The currently United States-licensed group C Neisseria meningitidis vaccine, composed of the O-acetyl-positive capsular polysaccharide, is poorly immunogenic and does not afford protection from disease to infants and young children. Group C N. meningitidis O-acetyl-negative polysaccharide vaccine induces higher titers in adults than does the O-acetyl-positive vaccine. We compared the immunogenicity of these vaccines in 2-year-old children. Reactions were minimal and did not differ between the two vaccines. The postvaccination geometric mean titer was twofold greater in the O-acetyl-negative group (1.58 versus 0.73 micrograms of antibody per ml). The rates of decline in titer were similar in both groups. Further study regarding immunogenicity of and the anamnestic response to the O-acetyl-negative vaccine is warranted in the age group (less than 18 months) at highest risk for invasive meningococcal disease.