To assess the efficacy of a 7-valent pneumococcal polysaccharide-meningococcal outer membrane protein complex conjugate vaccine (PncOMPC) against acute otitis media (AOM), 1666 infants were randomly assigned to receive either PncOMPC or control vaccine (hepatitis B vaccine) at 2, 4, 6, and 12 months of age. Of the 835 children assigned to receive PncOMPC, 187 received a 23-valent pneumococcal polysaccharide vaccine (PncPS) at 12 months of age instead. Whenever AOM was diagnosed, middle ear fluid was aspirated for bacterial culture. In the PncOMPC and control groups, there were 110 and 250 AOM episodes, respectively, in children between 6.5 and 24 months of age that could be attributed to vaccine serotypes, which indicates a vaccine efficacy of 56% (95% confidence interval, 44%-66%). The serotype-specific efficacy ranged from 37% for 19F to 82% for 9V. The 2 boosters seemed to provide equal protection against AOM, but PncPS induced markedly higher antibody concentrations. The efficacy of PncOMPC was comparable to that of the recently licensed pneumococcal conjugate vaccine.

Relative avidity of IgG to Streptococcus pneumoniae type 6B and 23F polysaccharides (PSs) was measured in sera of children immunized with pneumococcal vaccines, using an EIA and the chaotropic agent thiocyanate. Infants were immunized at 2, 4, and 6 months of age with pneumococcal PS-diphtheria toxoid conjugate vaccine, and boosted at 14 months with the homologous conjugate or a pneumococcal PS vaccine. The concentrations of antibodies to 6B and 23F PSs increased significantly after the booster with both vaccines. A significant increase in the avidity of anti-6B and anti-23F antibodies was seen after the booster with conjugate but not with PS vaccine. Avidity also increased in another group of infants primed and boosted with pneumococcal PS-meningococcal protein conjugate but not in a group boosted with PS vaccine after priming with pneumococcal PS-tetanus toxoid conjugate. In the latter group, however, the avidity of anti-6B was high before boosting.

Sixty-two infants and 31 toddlers were vaccinated with the tetravalent pneumococcal conjugate vaccine PncOMPC consisting of the capsular polysaccharide of pneumococcal types 6B, 14, 19F, and 23F conjugated to the outer membrane protein complex of Neisseria meningitidis. Infants were vaccinated at 2, 4, and 6 months (group A) or at 4, 6, and 14 months (group B); toddlers were vaccinated at 24 or at 24 and 26 months of age. The IgG responses to the four pneumococcal polysaccharide types were measured by EIA. In infants, types 14 and 19F induced a significant response after the first dose and types 6B and 23F after the second dose. A clearcut booster response was seen to the booster dose given at 14 months, indicating immunologic priming by the primary series at 2-6 months of age. The responses of the toddlers to one or two doses of the vaccine were very similar to the responses in infants.

The PncD conjugate vaccine is immunogenic and able to induce immunologic memory.