Studies on the combined administration of Haemophilus influenzae type B--diphtheria toxoid conjugate vaccine (PRP-D) and DTP.

The safety and immunogenicity of an Haemophilus influenzae type b capsular polysaccharide-diphtheria toxoid vaccine (PRP-D) has been evaluated when administered alone or simultaneously with other vaccines in over 1,400 2-24 month old subjects. In the first infant study, groups of subjects received either the PRP-D, PRP or placebo vaccine at 3, 5 and 7 months, one month after DPT immunization at 2, 4 and 6 months of age. In a subsequent study infants received either the PRP-D or PRP vaccine simultaneously with DPT. Safety of the PRP-D vaccine was indistinguishable from that of the PRP and placebo vaccines. In both studies, greater than 90% of the PRP-D recipients developed protective levels of antibody (greater than 0.15 microgram/ml) and the majority developed greater than 1.0 microgram/ml of anti-PRP. Following a booster dose of PRP-D at 14-18 months, simultaneously with either MMR, DPT or polio vaccine, all children in these studies developed greater than 1.0 micrograms/ml of antibody. Several other administration schedules have been evaluated in separate clinical studies. Acceptability of a combined DPT/PRP-D vaccine is currently being evaluated in experimental studies.