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 ≥ 0.15 μg/ml and 96 to 99% achieved high anti-PRP concentrations (≥ 1.0 μg/ml). The post-third dose anti-PRP geometric mean titer was high (6.94 μg/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 μg/ml) (P not significant). No differences were detected among the groups in tetanus antitoxin response, whereas after two or three doses the geometric mean titer of diphtheria antitoxin was significantly higher in the group who received PRP-T combined with DTP than in the group who received PRP-T as a separate inoculation (P < 0.016). Pertussis agglutinin, antitoxin and anti-filamentous hemagglutinin responses did not differ among the groups. These results encourage coadministration of PRP-T and DTP in a single inoculation, in view of the practical advantages of such combined immunization.
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AVENDAÑO et al. (1993) studied this question.