Immunogenicity of, and immunologic memory to, a reduced primary schedule of meningococcal C-tetanus toxoid conjugate vaccine in infants in the United kingdom

It has been previously shown that one of the three meningococcal C conjugate (MCC) vaccines introduced in the United Kingdom proved highly immunogenic after the first dose of a three-dose schedule, with evidence of immune memory after dose 3. Thus, in infants a one- or two-dose schedule of this MCC vaccine, conjugated to tetanus toxoid (TT), may suffice. Healthy infants ( n = 586) were randomized to receive either one (group 1), two (group 2), or three (group 3) doses of MCC-TT vaccine with a 10-μg polysaccharide booster given at 13 to 14 months of age. Serum bactericidal antibody (SBA) levels were measured by utilizing rabbit complement (rSBA), meningococcal C-specific immunoglobulin G (IgG), and avidity indices (AIs). For groups 1, 2, and 3, the percentages of infants with an rSBA level of ≥8 against strain C11 were 98.4, 100, and 99.4%, respectively. Infants in group 1 with prevaccination rSBA titers of ≥8 had post-primary MCC rSBA geometric mean titers (GMTs) significantly lower than those infants with prevaccination rSBA titers of