Immunogenicity of a Haemophilus influenzae type b vaccine in combination with diphtheria-pertussis-tetanus vaccine in infants.

Seventy-eight Navajo infants (one to two months of age) were randomly assigned to one of two vaccination groups: one group (40 infants) was scheduled to receive three doses of diphtheria-pertussis-tetanus (DPT) vaccine and the other (38 infants) to receive DPT combined with Haemophilus influenzae type b polyribosyl-ribitol phosphate (DPT + PRP vaccine). In the latter vaccine, pertussis antigen served as an adjuvant for PRP. Sixty-seven infants (37 who received DPT vaccine and 30 who received DPT + PRP vaccine) completed the protocol. Local and systemic reactions were equally frequent in the two groups. Fifty percent of the infants who received DPT + PRP vaccine had definite antibody responses to PRP after three doses, and 13% had possible responses. Of the infants who received DPT vaccine, 14% and 8% had definite and possible responses, respectively; three of five infants with definite responses were infected with H influenzae type b or cross-reacting organisms, as determined by pharyngeal cultures. The immune response did not appear to be suppressed by the presence of maternal antibody.