Further characterization of responses of infants and children to meningococcal A polysaccharide vaccine.

The responses to 10 or 50 microgram doses of meningococcal group A polysaccharide vaccine were evaluated in infants and children. Although the 50 microgram dose was shown to be more effective in the induction of detectable anti-A antibody in vaccinees of all ages, only 6.5% (7/108) of infants smaller than or equal to 12 months demonstrated a "protective level" (greater than or equal to 2 mug/ml antibody protein) at 28 or 35 days postinoculation. Unexpected variations in the response to different lots, supplied by three different manufactures, were observed. These findings indicate the need for additional studies before routine immunization of young infants can be recommended.