Priming for immunologic memory in adults by meningococcal group C conjugate vaccination.

Meningococcal group C polysaccharide-protein conjugate vaccines (MCV) prime infants and children for memory anticapsular responses upon subsequent exposure to unconjugated polysaccharide. The objective of this study was to determine whether MCV primes vaccine-naïve adults and adults previously vaccinated with meningococcal polysaccharide vaccine (MPSV) for memory antibody responses. Meningococcal vaccine-naïve adults were randomized to receive either MCV (MCV/naïve group) (n = 35) or pneumococcal conjugate vaccine (PCV) (PCV/naïve group) (n = 34). Participants with a history of receiving MPSV were given MCV (MCV/MPSV group) (n = 26). All subjects were challenged 10 months later with one-fifth of the usual dose of MPSV (10 mug of each polysaccharide). Sera were obtained before the conjugate vaccination and before and 7 days after the MPSV challenge and assayed for immunoglobulin G (IgG) anticapsular antibody concentrations and bactericidal titers. The MCV/naïve group had 7- to 10-fold-higher serum IgG and bactericidal responses after the MPSV challenge than the PCV/naïve group (P < 0.001). The increases (n-fold) in anticapsular antibody concentrations in the MCV/naïve group were greatest in subjects with antibody concentrations of <or=2 microg/ml before the challenge (geometric mean increase [n-fold] of 8.3 versus 1.1 in subjects with concentrations of >2 microg/ml before the challenge; P < 0.0001). Only 3 of 11 MCV-vaccinated subjects who had received MPSV before enrollment and who had antibody concentrations of <or=2 microg/ml before the polysaccharide challenge showed more-than-twofold increases in anticapsular antibody concentration or bactericidal titer after the challenge. MCV vaccination of meningococcal vaccine-naïve adults primes for robust memory antibody responses. There was no evidence of induction of memory by MCV in adults previously vaccinated with MPSV.