AVIDITY OF IGG FOR STREPTOCOCCUS-PNEUMONIAE TYPE 6B AND 23F POLYSACCHARIDES IN INFANTS PRIMED WITH PNEUMOCOCCAL CONJUGATES AND BOOSTED WITHPOLYSACCHARIDE OR CONJUGATE VACCINES

Relative avidity of IgG to Streptococcus pneumoniae type 6B and 23F po lysaccharides (PSs) was measured in sera of children immunized with pn eumococcal vaccines, using an EIA and the chaotropic agent thiocyanate . Infants were immunized at 2, 4, and 6 months of age with pneumococca l PS-diphtheria toroid conjugate vaccine, and boosted at 14 months wit h the homologous conjugate or a pneumococcal PS vaccine. The concentra tions of antibodies to 6B and 23F PSs increased significantly after th e booster with both vaccines. A significant increase in the avidity of anti-6B and anti-23F antibodies was seen after the booster with conju gate but not with PS vaccine. A vidity also increased in another group of infants primed and boosted with pneumococcal PS-meningococcal prot ein conjugate but not in a group boosted with PS vaccine after priming with pneumococcal PS-tetanus toroid conjugate. In the latter group, h owever, the avidity of anti-6B was high before boosting.