Immunogenicity of Haemophilus influenzae type b tetanus toxoid conjugate vaccine in young infants. The Kaiser-UCLA Vaccine Study Group.

In a prospective, randomized, double-blind efficacy trial, the immunogenicity of 10 lots of Haemophilus influenzae type b capsular polysaccharide-tetanus toxoid conjugate vaccine (PRP-T) was evaluated. More than 10,000 infants received PRP-T or hepatitis B vaccine at about 2, 4, and 6 months of age along with other childhood vaccines. In a subset of infants, geometric mean concentrations of total anticapsular antibody were 0.08, 0.79, and 5.29 micrograms/mL after the first, second, and third doses, respectively. Four lots of reconstituted lyophilized PRP-T vaccine were significantly more immunogenic than 6 lots of aqueous vaccine (P = .03). In a stepwise regression model, the most important additional factors affecting anticapsular antibody concentrations were the time between the third dose and the blood draw, race, and breast-feeding status at 6 months of age. Immune responses to diphtheria and tetanus toxoids were not significantly different for infants given PRP-T or hepatitis B vaccines along with diphtheria-tetanus toxoid-pertussis vaccine.