Influence of prior meningococcal C polysaccharide vaccination on the response and generation of memory after meningococcal C conjugate vaccination inyoung children

To determine whether the immunological hyporesponsiveness induced by mening ococcal AC polysaccharide (MACP) vaccines can be overcome by meningococcal C conjugate (MCC) vaccine in young children, serum bactericidal antibody (S BA) serogroup C-specific IgG and IgG avidity indices were measured in young children who received MACP vaccine, followed 7 months later by MCC vaccine , and their responses were compared with those in age-matched MACP-naive co ntrol children, who received a single dose of MCC vaccine. For children <1 year of age at MACP vaccination, the SBA geometric mean titer (GMT) after M CC vaccination was lower (P = .022) and proportions with SBA titers <8 (P = .0083)or <128 ( P = .0091) were higher than those in the control children. For older children, there was no difference in the SBA GMTs between the st udy and control groups (P > .5) or in the proportion with SBA titers <8 (P = 1.00) or <128 (P = .98). No increase in avidity occurred after MACP vacci nation, whereas avidity increased significantly 1 month after MCC vaccinati on, with a further increase at 6 months, which indicates that the induction of immunological memory was not impaired.