The safety, immunogenicity, and immunologic priming of 2 dosages (2 microgram or 10 microgram) of a meningococcal C oligosaccharide-CRM197 conjugate vaccine was evaluated in 114 infants vaccinated at ages 2, 3, and 4 months. Antibody persistence and response to boosting with 10 microgram of meningococcal C polysaccharide were assessed. The meningococcal conjugate vaccine produced fewer local reactions than concurrent routine immunizations. Total serogroup C-specific immunoglobulin geometric mean concentration (GMC) increased from 0.3 microgram/mL before vaccination to 13.1 microgram/mL at age 5 months. Serum bactericidal antibody (SBA) geometric mean titers (GMTs) rose from <1:4 to 1:1057 at 5 months and fell by 14 months to 1:19. Following boosting, anti-C-specific immunoglobulin GMC rose to 15.9 microgram/mL and SBA GMT to 1:495. Antibody responses in the 10-microgram dose cohort were significantly higher at 5 months (P<.01) than in the 2-microgram dose cohort but were lower after polysaccharide boosting (P=.02). This meningococcal conjugate vaccine was well tolerated and immunogenic and induced immunologic memory in infants.

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The reactogenicity and immunogenicity of a serogroup A and C meningococcal polysaccharide-CRM197 conjugate vaccine was evaluated in 58 infants who received three doses at 2, 3, and 4 months of age. The conjugate vaccine produced few systemic side effects, and local reactions were significantly less common than those produced by the routine vaccinations. The prevaccination geometric mean titers (GMTs) of A and C polysaccharide antibodies were, respectively, 2.8 and 0.6 microg/mL, rising to 21.5 and 38.5 microg/mL by 1 month after the third dose (age 5 months) and falling to 3.1 and 2.2 mircog/mL by 14 months of age. Prevaccination serum bactericidal titers against 2 serogroup C meningococci strains were <1/4 in 49 of 52 infants, rising to a GMT of 1/3082 at 1 month after the third dose and falling by age 14 months to a GMT of 1/10. Thus, this meningococcal conjugate vaccine proved to be safe and immunogenic, inducing high levels of anti-C polysaccharide antibodies that were bactericidal in young infants.

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