- Anttila M,
- Eskola J,
- Ahman H,
- Kayhty H
Purpose of the Study
To assess possible differences in avidity maturation of antipneumococcal polysaccharide (PS) antibodies between infants boosted with the conjugate and those boosted with the PS vaccine.
Seventy-five healthy infants were vaccinated, and sera were analyzed from 71 infants.
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. Relative avidity of immunoglobulin G (IgG) to Streptococcus pneumoniae type 6B and 23F PSs was measured in sera of these children using an EIA and the chaotropic agent thiocyanate. Sera were also analyzed from previous immunogenicity studies in another group of infants primed and boosted with pneumococcal PS-meningococcal protein conjugate and compared with a group boosted with PS vaccine after priming with the pneumococcal PS-tetanus toxoid conjugate.
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 observed after the booster with conjugate but not with PS vaccine. Avidity also increased in the other group of infants primed and boosted with pneumococcal PS-meningococcal protein conjugate but not in the group boosted with PS vaccine after priming with pneumococcal PS-tetanus toxoid conjugate. In the latter group, the avidity of anti-6B was high before boosting.
The relative avidity of IgG to S pneumoniae type 6B and 23F PSs increased in infants primed with conjugate vaccines when boosted with conjugated but not PS vaccine.
Protein conjugate vaccines are T cell-dependent whereas PS vaccines are T cell-independent. As observed in Haemophilus influenzaetype b conjugate vaccines, induction of T cell response allows pneumococcal conjugate vaccines to be immunogenic in infants, to induce immunologic memory and to enhance avidity with booster doses.