INTERCHANGEABILITY OF CONJUGATED HAEMOPHILUS-INFLUENZAE TYPE-B VACCINES IN INFANTS

Objective.-To evaluate the safety and immunogenicity of two Haemophilus influenzae type b (Hib) conjugate vaccines when administered in serial combination, These vaccines consisted of Hib capsular polysaccharide polyribosyl-ribitol phosphate (PRP) conjugated to the meningococcal outer membrane protein (OMP) complex (PRP-OMP) and H influenzae oligosaccharide conjugated to a mutant toxin (CRM197) isolated from Corynebacterium diphtheriae (HbOC). Design.-Randomized, double-blind, clinical trial evaluating five Hib vaccination regimens. Setting.-Vaccine Treatment and Evaluation Units and affiliated private pediatric practices at Saint Louis (Mo) University, Vanderbilt University, Nashville, Tenn, and Baylor College of Medicine, Houston, Tex. Patients.-A total of 497 healthy 2-month-old infants scheduled to receive routine immunization. Intervention.-Participants received either PRP-OMP or HbOC given as recommended by the manufacturer, PRP-OMP at 2 and 6 months, HbOC at 2 months, then PRP-OMP at 4 and 6 months, or PRP-OMP at 2 months and then HbOC at 4 and 6 months. Unconjugated PRP was given at 15 months to evaluate priming. Results.-Geometric mean antibody concentrations differed significantly among the groups following the second and third immunizations of the primary series and following booster immunization with unconjugated PRP. On each occasion, the groups receiving serial combinations of PRP-OMP and HbOC achieved mean antibody concentrations that equalled or exceeded those of the groups receiving a single product. Adverse reactions did not vary by group. Conclusions.-The studied sequential combinations of Hib vaccines were safe and at least as immunogenic as either vaccine alone.