ANTIBODY-AFFINITY IN INFANTS AFTER IMMUNIZATION WITH CONJUGATED CAPSULAR POLYSACCHARIDE FROM HAEMOPHILUS-INFLUENZAE TYPE-B

The affinities of IgG antibodies to Haemophilus influenzae b capsular polysaccharide (polyribosyl ribitol phosphate [pRP]) elicited 1 month after immunization of 47 infants 2->18 months of age with a PRP-outer membrane protein conjugate (PRP-OMP) were measured by ELISA. Thirty-four sera had affinities distributed normally about a logarithmic mean of 3.2 × 105 l/mol, but 13 samples had undetectable affinities <104 l/mol). Median affinities of sera from children 2–6 (1.5 × l05 l/mol) and 7–11 months of age (1.6 × 105 l/mol) were significantly greater than the median affinities of sera from infants 12–18 (1.8 × 104 l/mol) or >18 months of age (4.2 × 104 l/mol). Sera from children >18 months of age vaccinated with PRP conjugated to diphtheria toxoid had a median affinity of 6.1 × 104 l/mol, equivalent to that of the same age group vaccinated with PRP-OMP. Children vaccinated with PRP conjugate vaccines may produce antibodies ofvery low affinity, a finding that may have significance for protection from invasive disease. © 1990, by The University of Chicago.