SAFETY AND IMMUNOGENICITY OF AN HAEMOPHILUS-INFLUENZAE TYPE B-TETANUSTOXOID CONJUGATE (PRP-T) AND DIPHTHERIA-TETANUS-PERTUSSIS (DTP) COMBINATION VACCINE ADMINISTERED IN A DUAL-CHAMBER SYRINGE TO INFANTS IN BELGIUM AND CHILE

To document any unexpected differences in the immune response between study populations and to evaluate immunogenicity and safety of a simpl ified presentation (dual-chamber syringe) of an Haemophilus influenzae type b-tetanus toroid conjugate (PRP-T) and diphtheria-tetanus-pertus sis (DTP) combination vaccine, a multi-centre, randomized, comparative study was conducted in Belgium and Chile. A total of 537 healthy infa nts, 270 in Chile and 267 in Belgium, received PRP-T and DTP vaccines combined in a dual-chamber syringe (D-Ch group, DTP/PRP-T, reconstitut ed by pressing the plunger of the syringe immediately before injection , n =239) or combined in a single-chamber syringe (C-In group, DTP//PR P-T; reconstituted immediately before injection, n = 61) or in separat e injections (S-In group, DTP+PRP-T, simultaneously injected at separa te sites, n = 237) at 3, 4, and 5 months of age. Serum samples were co llected before vaccination and at 6 months of age. In the D-Ch group, the incidence of adverse events was comparable to administration of DT P vaccine alone. Higher rates of local and systemic reactions were obs erved in the Chilean population possibly due to differences in surveil lance practice. The immune response to each vaccine component compared well to that of the separate administration of PRP-T and DTP vaccines , except for higher post-immunization anti-PRP geometric mean titre (G MT) values after separate injections (25.6 mu g mL(-1)) than after (p = 0.001). An combined injection with the dual-chamber syringe (17.6 mu g mL(-1)) (p = 0.001). An unexpected 'syringe' effect was seen: a gre ater post-immunization anti-PRP GMT was observed in the D-Ch group (17 .6 mu g mL(-1)) than in the C-In group (7.7 mu g mL(-1)) (p = 0.0001). Whereas pre-immunization GMTs of some antibodies we-e significantly l ower in Chilean than in Belgian infants, the post-immunization GMTs of Chilean infants were two to three times greater for all of the antibo dies studied (p < 0.005). Differences in reactogenicity and in the imm une response between the study populations or the different vaccine pr esentations were striking, but are probably of no clinical relevance. Tire convenient dual-chamber syringe presentation of DTP and PRP-T vac cines is safe and highly immunogenic. (C) 1998 Elsevier Science Ltd. A ll rights reserved.