INDUCTION OF IMMUNOLOGICAL 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 diseas e, because of poor immunologic responses to the Neisseria meningitidis serogroup C polysaccharide in these age groups. Meningococcal C conju gate vaccines offer the prospect of circumventing this problem. Object ive.-To assess the immunogenicity and the induction of immunologic mem ory in toddlers by meningococcal C conjugate vaccine. Design.-A multic enter, randomized, observer-blinded controlled trial. Setting.-Urban a nd suburban family medicine or pediatric practices, Participants.-Two hundred eleven healthy toddlers aged 15 to 23 months. Intervention.-Tw o injections at 2 months apart of meningococcal C conjugate (group 1, n = 69), plain meningococcal polysaccharide (group 2, n = 72), or hepa titis B virus vaccine (group 3, n = 70). All toddlers received a follo w-up dose of plain meningococcal polysaccharide vaccine 12 months late r. Main Outcome Measures.-IgG meningococcal C anticapsular antibody co ncentrations determined by enzyme-linked immunosorbent assay and compl ement-mediated bactericidal antibody. Results.-In group 1, the magnitu de of the IgG response to meningococcal C conjugate vaccine was more t han 4-fold higher after dose 1 and more than 10-fold higher after dose 2 compared with meningococcal polysaccharide vaccine (group 2) (P<.00 1). Higher titers persisted in the meningococcal C conjugate group for at least 12 months (P<.001). Group 1, primed with meningococcal C con jugate, had 25-fold higher IgG responses to the meningococcal polysacc haride 1-year booster dose than the controls who had received hepatiti s B virus vaccine initially and were given meningococcal polysaccharid e vaccine 1 year later for the first time (P<.001). In contrast, group 2, primed with meningococcal polysaccharide, had a 2-fold lower respo nse to the 1-year booster meningococcal polysaccharide dose than the h epatitis B virus control group (P=.006), Serum bactericidal responses paralleled the enzyme-linked immunosorbent assay responses. Conclusion s.-Immunization of toddlers with meningococcal C conjugate vaccine ind uces high titers of anticapsular and bactericidal antibody. Furthermor e, this vaccine induces immunologic memory to meningococcal C polysacc haride. In contrast, meningococcal polysaccharide vaccine is less immu nogenic than the conjugate vaccine and also induces a hyporesponsive s tate that persists for at least 12 months.