AGE-DEPENDENT NEISSERIA-MENINGITIDIS SEROGROUP-C CLASS-SPECIFIC ANTIBODY CONCENTRATIONS AND BACTERICIDAL TITERS IN SERA FROM YOUNG-CHILDRENFROM MONTANA IMMUNIZED WITH A LICENSED POLYSACCHARIDE VACCINE

Neisseria meningitidis serogroup C bactericidal titers and class-speci fic enzyme-linked immunosorbent assay (ELISA) antibody concentrations were measured in sera from 173 children (1 to 5 years old) before and 6 weeks and 7 months following vaccination with a quadrivalent (A/C/Y/ W-135) polysaccharide vaccine. The immune responses of the children we re compared with those of 40 adults 6 weeks postvaccination. Both bact ericidal titers and ELISA antibody concentrations were significantly h igher in the adults than in the children (P < 0.05). In addition, the ratio of immunoglobulin G (IgG) to IgM was higher in the children than in the adults. With an ELISA total antibody concentration of greater than or equal to 2 mu g/ml used as a measure of seroconversion, greate r than or equal to 84% of the individuals from each age group responde d to the serogroup C polysaccharide. However, with a greater than or e qual to 4-fold-increase in bactericidal titer used, only 18% of 1-year olds, 32% of 2-year-olds, and 50 to 60% of 3-, 4-, and 5-year-olds se roconverted. The ELISA results suggest that >50% of all children retai ned greater than or equal to 2 mu g of total antibody per mi at 7 mont hs postimmunization. However, the bactericidal titers suggest that < 1 0% of children <4 years old retained a greater than or equal to 4-fold increase at 7 months following vaccination. Of particular note, 59 of 79 sera (75%) from the 1- and 2-year-olds had high ELISA antibody con centrations (2 to 20 mu g/ml) with no associated bactericidal titer (< 1:8). Discordant results between bactericidal titers and ELISA antibod y concentrations were not explained by the presence of IgA blocking an tibody or relative levels of IgG and IgM. The bactericidal results sho w age-dependent differences in the production and retention of antibod y in young children immunized with serogroup C polysaccharide; these d ifferences are not evident with the ELISA data.