IMMUNOGENICITY OF HAEMOPHILUS-INFLUENZAE TYPE-B POLYSACCHARIDE TETANUS TOXOID CONJUGATE VACCINE IN INFANTS

Objective.-To compare the safety and immunogenicity of three investigational lots of Haemophilus influenzae type b polysaccharide-tetanus toxoid (PRP-T) conjugate vaccine in infants. Design.-A multicenter, randomized immunogenicity trial. Infants were vaccinated at 2, 4, and 6 months of age with one of three lots of PRP-T. A control group received H influenzae type b oligomers conjugated to CRM197 (HbOC). Serum was obtained before each injection and 1 month after the third dose, and assayed blindly for antibody in one laboratory. Subjects.-Four hundred eighty-four infants from private pediatric practices located in five geographic areas. Measurements and Results.-There were no significant differences in the number of adverse events reported for infants receiving PRP-T or HbOC, and the rates did not exceed those observed previously in infants given diphtheria-tetanus-pertussis vaccine alone. Total serum anti-PRP antibody responses were analyzed in 336 infants who met strict inclusion criteria. After one, two, or three doses, the respective antibody responses to each of the three lots of PRP-T and to HbOC vaccine were similar. The only exception was one lot of PRP-T, which after one or two injections elicited significantly higher geometric mean antibody responses than the other two lots or the HbOC vaccine. After a third injection, there were no significant lot differences. Combining the data from the different lots, there were no significant differences in the geometric mean antibody concentration after three doses of PRP-T or HbOC (8.3 vs 7.7 mug/mL), and 95% and 91 %, respectively, of infants had greater than 1.0 mug/mL of antibody. There were no significant differences in the magnitudes of the respective IgG1-, IgG2-, and IgM-specific antibody concentrations between infants given PRP-T or HbOC. Conclusions.-The three investigational lots of PRP-T tested were safe and were as immunogenic as or more so than the licensed HbOC conjugate vaccine.