Immunogenicity and Safety of a Quadrivalent Meningococcal ACWY-tetanus Toxoid Conjugate Vaccine 6 Years After MenC Priming as Toddlers.

Background: We assessed immunogenicity, antibody persistence and safety of the meningococcal serogroups A, C, W and Y-tetanus toxoid (TT) conjugate vaccine (MenACWY-TT) in children primed as toddlers with MenC vaccine. Methods: This open, multicenter extension study enrolled children 84-95 months of age who had received one dose of the combined Haemophilus influenzae type b (Hib)-MenC-TT conjugate vaccine (HibMenC group) or Hib-TT and monovalent MenC (MCC)-CRM 197 vaccines (Hib+ MCC group) at 12-18 months of age, in the primary study. All participants received one dose of Men-ACWY- TT. We assessed immunogenicity against MenA, MenC, MenW and MenY at 1 month and 2 years postvaccination by serum bactericidal assay using baby rabbit complement (rSBA). Safety and reactogenicity were evaluated. Results: Six years post-MenC vaccination, <20% of children retained rSBA-MenC titers >= 1:8. At 1 month post-MenACWY-TT vaccination, vaccine response rates against all serogroups were high for both groups with >= 97.1% of children having rSBA >= 1: 8. Two years postvaccination, = 63.6% of children retained rSBA-MenA >= 1: 8, and >= 87.9% for other serogroups. Geometric mean titers for all serogroups declined at 2 years post-MenACWY-TT vaccination, but remained >= 13 times higher than prevaccination levels. For both groups, pain (<= 58.5%), redness (<= 51.4%) and fatigue (<= 27.0%) were the most frequently reported adverse events. No serious adverse events were reported. Conclusions: One dose of MenACWY-TT boosts protection against MenC in primed children, is safe and extends protection against MenA, MenW and MenY. Immunogenicity and safety were comparable in infants vaccinated with conjugated vaccine (HibMenC-TT) or the separate vaccines (Hib-TT and MCC-CRM 197).