Evaluation of two tetravalent (ACYW135) meningococcal vaccines in infants and small children: a clinical study comparing immunogenicity of O-acetyl-negative and O-acetyl-positive group C polysaccharides.

Two different tetravalent polysaccharide vaccines against group A, C, Y, and W135 meningococci were given to 118 infants aged 6 to 23 months; the same vaccines were administered in a second dose 12 months later to those infants aged 6 to 11 months at first vaccination. Forty of the infants received vaccine containing the nonacetylated group C polysaccharide C(OAc-) and 78 the acetylated group C polysaccharide C(OAc+) together with group A, Y, and W135 polysaccharides. All polysaccharides, at a dose of 30 micrograms, induced antibody responses after administration of both vaccines in all age groups although the responses were better in the older infants. Acetylation of the sialic acid of the group C polysaccharide did not significantly influence the response. Rapid decreases in the antibody titers after the first vaccination stressed the need for one or more revaccinations. Vaccination elicited mild local and systemic reactions. Elevated temperatures were more common in the youngest infants but only four developed fever exceeding 38.5 degrees C (101.3 degrees F). We conclude that tetravalent (ACYW135) meningococcal vaccine is safe and immunologically effective in children younger than age 2 years. However, revaccinations may be required to maintain immunity.