IMMUNOGENICITY OF TWO PNEUMOCOCCAL CONJUGATE VACCINES • 766

Abstract

To assess the immunogenicity of octavalent pneumococcal vaccines that contained either 3 μg of each serotype conjugated to diphtheria toxoid(PncD) or 1 μg of each serotype conjugated to tetanus toxoid (PncT), 80 infants (20 at each of 4 sites) were enrolled to receive one of these vaccines(a total of 40 infants for each vaccine) given separately but at the same time as other routine immunizations (PRP-T, DTP and OPV) at 2, 4 and 6 months of age. Antibody concentrations before each dose and one month after the third dose were determined by ELISA (after adsorption of serum to C-polysaccharide) by Connaught Laboratories. Adverse side effects were minimal. The geometric mean concentrations (GMT) of IgG antibody (μg/ml) against each serotype and against PRP are shown below. Both vaccines induced significant (P<0.05, and in most instances <0.001) increases in concentrations of antibody against each serotype of pneumococcus (except for PncT against type 9V); GMTs of IgG at 7 months against serotypes 4, 6B and 9V were significantly higher in infants who had received PncT than in those who had received PncD (P<0.003). We conclude that both PncD and PncT induce significant increases in concentrations of serotype-specific anti-pneumococcal antibodies. Concentrations of type-specific antibodies at 7 months of age among children who received PncT were similar to or greater than those of children who received PncD. Table