Functional affinity of antibody to the Haemophilus influenzae type b polysaccharide

The functional affinity, or avidity, of antibody to the capsular polysaccharide of Haemophilus influenzae (Hib-PS) was measured in serum samples from 12 adult male subjects before and after immunization with Hib-PS vaccine. Mean avidity increased from 0.74 nM-1 to 1.5 nM-1 after immunization (P less than .05, paired Student's t test). The Bureau of Biologics reference antiserum had an avidity constant of 12 nM-1, which was the highest of all 25 serum samples studied.