Administration of combined diphtheria and tetanus toxoids and pertussis vaccine, hepatitis B vaccine, and Haemophilus influenzae type b (Hib) vaccine to infants and response to a booster dose of Hib conjugate vaccine.

We compared antibody levels following separate but simultaneous administration of diphtheria and tetanus toxoids with acellular pertussis vaccine (DTaP) containing pertussis toxoid, filamentous hemagglutinin, and pertactin (PRN); hepatitis B vaccine; and Haemophilus influenzae type b polysaccharide (polyribosylribitol phosphate; PRP) vaccine conjugated to tetanus toxoid (PRP-T) with those following administration of a combination of a DTaP-hepatitis B vaccine-PRP-T to infants at 2, 4, and 6 months of age. The antibody response to a booster dose of PRP conjugate vaccine (CRM197-OS) in infants with low (< 1 microgram/mL) or undetectable (< 0.10 microgram/mL) postpriming levels of antibody to PRP was also studied. Antibody levels were quantitated before and after dose 3 by enzyme-linked immunosorbent assay, radioimmunoassay, or neutralization assay. Seroresponse rates were not different between the two vaccine groups except for rates of response to PRP. There was a trend that levels of antibody to all the antigens included in the combination vaccine were lower than those of antibody to antigens in separate vaccines; for levels of antibody to diphtheria toxoid (P = .001), PRN (P < .0001), and PRP (P < .0001), the differences were significant. Despite low or undetectable postpriming levels of antibody to PRP, high-titered (geometric mean concentration, 9.02 micrograms/mL; range, 1.0-81.5 micrograms/mL), immunoglobulin G-predominant antibody to PRP was produced following a booster dose of CRM197-OS, a finding consistent with a memory response.