Ability of 3 different meningococcal C conjugate vaccines to induce immunologic memory after a single dose in UK toddlers

To test for immunologic memory after a single dose of meningococcal C conju gate (MCC) vaccine in toddlers, 226 children 12-18 months old were randomiz ed to receive 1 of 3 MCC vaccines, with a C polysaccharide booster 6 months later. The protein conjugate was diphtheria mutant toxoid in 2 vaccines (M CC-CRM197) and was tetanus toxoid in the third (MCC-TT). One month after th e MCC vaccines, 91%-100% of children had serum bactericidal antibody (SBA) titers greater than or equal to8, and 89%-100% had a greater than or equal to4-fold increase. Geometric mean titer (GMT) increased from <4 to 215 (95% confidence interval [CI], 166-279). MCC-TT induced higher SBA GMTs (P<.001 ) and higher proportions with SBA greater than or equal to8 (P=.02) than di d the MCC-CRM197 vaccines. By 6 months, GMTs had decreased to 55.1 (95% CI, 40-76), but IgG antibody avidity increased (P<.001). Induction of immunolo gic memory was confirmed by a GMT of 1977 (range, 1535-2547) after the poly saccharide booster and a further increase in avidity. This evidence justifi ed the use of a single dose in a catch-up immunization program for children 1-18 years old.