Induction of Immunologic Memory by Conjugated vs Plain Meningococcal C Polysaccharide Vaccine in Toddlers: A Randomized Controlled Trial

CONTEXT.— Meningococcal polysaccharide vaccines are not used routinely in infants and toddlers, the groups at highest risk of invasive disease, because of poor immunologic responses to the Neisseria meningitidis serogroup C polysaccharide in these age groups. Meningococcal C conjugate vaccines offer the prospect of circumventing this problem. OBJECTIVE.— To assess the immunogenicity and the induction of immunologic memory in toddlers by meningococcal C conjugate vaccine. DESIGN.— A multicenter, randomized, observer-blinded controlled trial. SETTING.— Urban and suburban family medicine or pediatric practices. PARTICIPANTS.— Two hundred eleven healthy toddlers aged 15 to 23 months. INTERVENTION.— Two injections at 2 months apart of meningococcal C conjugate (group 1, n=69), plain meningococcal polysaccharide (group 2, n=72), or hepatitis B virus vaccine (group 3, n=70). All toddlers received a follow-up dose of plain meningococcal polysaccharide vaccine 12 months later. MAIN OUTCOME MEASURES.— IgG meningococcal C anticapsular antibody concentrations determined by enzyme-linked immunosorbent assay and complement-mediated bactericidal antibody. RESULTS.— In group 1, the magnitude of the IgG response to meningococcal C conjugate vaccine was more than 4-fold higher after dose 1 and more than 10-fold higher after dose 2 compared with meningococcal polysaccharide vaccine (group 2) (P