The induction of immunologic memory after vaccination with Haemophilus influenzae type b conjugate and acellular pertussis-containing diphtheria, tetanus, and pertussis vaccine combination

The significance of reduced antibody responses to the Haemophilus influenza e type b (Hib) component of acellular pertussis-containing combination vacc ines (DTaP-Hib) is unclear. A DTaP-Hib vaccine evaluated in infants vaccina ted at ages 2, 3, and 4 months showed reduced anti-Hib polysaccharide IgG ( geometric mean concentration [GMC], 1.23 mu g/mL; 57%, >1.0 mu g/mL). Polyr ibitolribosyl phosphate (PRP) and Hib conjugate (PRP-T) vaccine given as a booster during the second year of life was evaluated for the presence of im munological memory. After boosting, most children achieved anti-PRP IgG >1. 0 mu g/mL, although the GMC was higher with PRP-T (88.5 mu g/mL) than with PRP vaccine (7.86 mu g/mL, P < .001). The GMC of the PRP group was higher t han anticipated for naive PRP recipients of the same age. PRP-specific IgG avidity was significantly higher after boosting than after priming, providi ng further evidence for the generation of memory. Despite reduced immunogen icity, DTaP-Hib combination vaccines appear to prime for immunologic memory .