VACCINE ANTIGEN INTERACTIONS AFTER A COMBINATION DIPHTHERIA-TETANUS TOXOID-ACELLULAR PERTUSSIS PURIFIED CAPSULAR POLYSACCHARIDE OF HAEMOPHILUS-INFLUENZAE TYPE-B-TETANUS TOXOID VACCINE IN 2, 4 AND 6-MONTH-OLD INFANTS/

Objective. The safety and immunogenicity of a diphtheria-tetanus toxoi d-acellular pertussis vaccine (DTaP; Trepedia(R))/Haemophilus influenz ae b polysaccharide (PRP-T; ActHib(R)) combined vaccine (TriHibir(R); Pasteur Merieux Connaught) was compared with DTaP and PRP-T given at t he same visit but at separate sites in a prospective multicenter, open label trial. Methods. Infants were randomized to four groups (three c onsistency lots of DTaP/PRP-T vs. one of the consistency lots given as separate vaccines); injections were administered at 2, 4 and 6 months of age. Pre-Dose 1 and post-Dose 3 sera were assayed for antibody tit ers against all antigens. Reactions to the vaccinations were assessed by parent questionnaire for 30 days after each injection visit. Result s. Four hundred eighty-five infants were enrolled; 296 evaluable infan ts were included in the DTaP/PRP-T group compared with 70 infants in t he DTaP and PRP-T vaccine group. Infants who received the combined vac cine had higher post-Dose 3 geometric mean antibody titers to diphther ia antitoxin (P < 0.01) and pertussis filamentous hemagglutinin (P < 0 .05) and lower geometric mean antibody titers to tetanus antitoxin (P < 0.05) and Haemophilus influenzae b (Hib) polysaccharide (PRP) (P < 0 .05). The geometric mean anti-PRP antibody titer in the DTaP/PRP-T gro up was 4.3 mu g/ml compared with 7.0 mu g/ml in the separate vaccine g roup (P < 0.05), and the percentage of infants with antibody titers gr eater than or equal to 0.15 and 1 mu g/ml were, respectively, 95 and 8 6%, whereas they were 100% for both titers in the separate vaccines gr oup. DTaP/PRP-T vaccine given concomitantly or 1 month apart from hepa titis B vaccine and oral poliomyelitis vaccine caused no significant d ifferences in immunogenicity or safety. The safety assessments for the DTaP/PRP-T vaccine showed no consistent differences in systemic or lo cal injection site reactions compared with DTaP and PRP-T administered separately. Conclusion. Although the antibody responses to tetanus an d Hib polysaccharide in the evaluated DTaP/PRP-T combined vaccine were significantly lower than those seen after separate DTaP and PRP-T adm inistration, the combined vaccine elicited an immune response against diphtheria, tetanus, pertussis and Haemophilus influenzae b likely to confer protection.