Two hundred seventy-five infants were randomly assigned to receive either DTaPH or a Diphtheria-Tetanus-Acellular Pertussis Vaccine (DTaP) and one of two Hib conjugate vaccines as separate injections. DTaPH contained either 25 or 50 μg of pertussis toxoid (PT), 3 μg of filamentous hemagglutinin(FHA), 10 lf of diphtheria (diph), and either 5, 2.5, or 1 lf of tetanus(tet) and 10 μg of Hib-tetanus conjugate vaccine(mHib-T). Connaught DTaP vaccine(23 μg each of PT and FHA, 6.7 lf diph, 5 lf tet) and either 10 μg of mHib-T or Wyeth-Lederle Hib-CRM197 conjugate vaccine (HbOC) were given in the separate injection groups. Each infant received the same vaccines as 0.5 ml IM injections in the anterolateral thighs at 2, 4, and 6 months. Other routinely recommended vaccines were also given. Immune responses to Hib by Farr assay 1 month after the third set are indicated in the table below. Immune responses to mHib-T and HbOC were comparable. GMC to Hib after DTaPH was lower than that obtained after mHib-T(p <.05) and after HbOC, although statistical significance was not achieved with the latter. The percentage of patients with ≥.15 μg/dl was similar after DTaPH and the separate vaccines; the percentage with ≥ 1.0 μg/dl was less after DTaPH than mHib-T (p <.05) and also after HbOC, although statistical significance was not achieved with the latter. Reducing the amount of tetanus did not improve Hib responses. This study suggests combining mHib-T and DTaP as a single formulation (DTaPH) diminished Hib antibody response when used as the primary series in infancy.

Table 1 No caption available.
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