Response of infants to Haemophilus influenzae type b polysaccharide and diphtheria-tetanus-pertussis vaccines in combination.

In a multicenter study, responses to a combined vaccine containing standard diphtheria-tetanus-pertussis (DTP) and polyribosylribitol phosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b, were evaluated in 107 infants who received single doses at two, four, and six months of age and compared with those in 61 infants given single doses of DTP alone on the same schedule. Reaction rates were comparable in the two treatment groups. At seven months of age 61% of the subjects given the combined DTP-PRP vaccine and 8% and of those given DTP alone showed an antibody response to PRP, as defined as a twofold increase in titer over the lowest previous level. Among those given the DTP-PRP combined vaccine, 92% of the positive antibody responses occurred after the third dose. There was a variation in antibody response, possibly due to a difference in the vaccine lots administered.