Haemophilus influenzae type b polysaccharide-tetanus protein conjugate vaccine does not depress serologic responses to diphtheria, tetanus or pertussis antigens when coadministered in the same syringe with diphtheria-tetanus-pertussis vaccine at two, four and six months of age.

The safety and immunogenicity of a vaccine against Haemophilus influenzae type b consisting of purified polyribosylribitol phosphate conjugated to tetanus toxoid (PRP-T) were evaluated in 277 Chilean infants who were randomly assigned to one of three treatment groups: Group A, PRP-T mixed with diphtheria-tetanus-pertussis (DTP) vaccine in a single syringe and given as a single inoculation in one arm and placebo in the other arm; Group B, PRP-T given in one arm and DTP in the other arm; Group C, DTP given in one arm and placebo in the other. Infants were immunized at 2, 4 and 6 months of age and examined daily for 4 days after each immunization. Serum PRP antibodies; tetanus, diphtheria and pertussis antitoxin; pertussis agglutinins; and antibodies to Bordetella pertussis filamentous hemagglutinin were measured at baseline and 2 months after each dose. PRP-T was well-tolerated. After three doses of PRP-T vaccine 100% of infants attained PRP antibody concentrations > or = 0.15 micrograms/ml and 96 to 99% achieved high anti-PRP concentrations (> or = 1.0 micrograms/ml). The post-third dose anti-PRP geometric mean titer was high (6.94 micrograms/ml) in infants who were given PRP-T combined with DTP, although it was somewhat lower than the geometric mean titer of the group who received PRP-T in a separate arm (9.93 micrograms/ml) (P not significant).(ABSTRACT TRUNCATED AT 250 WORDS)