ANTIBODY-RESPONSE AFTER IMMUNIZATION OF BRAZILIAN CHILDREN WITH SEROGROUP-C MENINGOCOCCAL POLYSACCHARIDE NONCOVALENTLY COMPLEXED WITH OUTER-MEMBRANE PROTEINS

We have studied the antibody response of Brazilian vaccinees to C meni ngococcal polysaccharide (C-PS) after one or two doses of a vaccine co mposed of C-PS, outer membrane proteins of B meningococci and aluminum hydroxide. Total IgG, IgG1 and IgG2 as well as bactericidal activity mediated by complement were measured in serum samples from children 3 to 83 months of age (postvaccination IgG, IgG1 and IgG2 levels of 2.4 to 13.4 mu g/ml; less than 18 to 67.8 U/ml and less than 18 to 106.8 U /ml, respectively) and from individuals 10 to 14 years of age (post-va ccination IgG, IgG1 and IgG2 levels of 14.6 mu g/ml, 23.7 U/ml and 112 .0 U/ml, respectively). The antibody response, measured as IgG levels, was age-dependent. Although high antibody levels were demonstrable by enzyme-linked immunosorbent assay (ELISA), bactericidal activity was not demonstrable (less than 1:4 in serum from children aged less than 24 months. A significant bactericidal activity was detected in serum o f children older than 49 months of age and in individuals 10 to 14 yea rs of age. A predominance of IgG2 was observed in post-vaccination ser um samples from children belonging to those two age groups. The antibo dy concentration sufficient to confer protection as well as the possib le causes of the poor correlation observed between ELISA and bacterici dal activity results are discussed.