Immunogenicity and immunological priming of the serogroup a portion of a bivalent meningococcal A/C conjugate vaccine in 2-year-old children

Two-year-old children were vaccinated with 1 dose of meningococcal A/C conjugate ( MACC) or meningococcal A/C polysaccharide ( MACP) vaccine. Meningococcal serogroup A (MenA)-specific IgG geometric mean avidity indices (GMAIs) increased 1 month after vaccination with MACC (GMAI, 210; 95% confidence interval [CI], 140-300) and MACP ( GMAI, 190; 95% CI, 120-310). One year after vaccination, the GMAI of the MACP-vaccinated cohort decreased to 130 ( 95%, CI 100-170), but a constant GMAI was maintained in the MACC-vaccinated cohort ( 210; 95% CI, 140-300), despite declining MenA-specific IgG antibody levels.