Priming with diphtheria-tetanus-pertussis vaccine enhances the response to the Haemophilus influenzae type b tetanus conjugate vaccine in infancy.

Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) conjugated to tetanus toxoid (PRP-T) was given at 4 and 6 months of age and anti-Hib PS antibody response to the first and second dose of PRP-T was compared in groups that received diphtheria-tetanus-pertussis (DTP) vaccine either simultaneously with PRP-T (34 infants) or separately at 3, 4 and 5 months of age (49 infants). The geometric mean anti-Hib PS antibody concentration after the first dose of PRP-T given at 4 months of age was eightfold higher if the infants primed with DTP at 3 months of age than if the first dose of DTP was given together with the first dose of PRP-T (0.81 microgram ml-1 vs 0.11 microgram ml-1). The positive influence of DTP priming was seen also after the second dose of PRP-T given at 6 months of age (7.55 micrograms ml-1 vs 3.45 micrograms ml-1).