Immunogenicity and reactogenicity of diphtheria, tetanus and pertussis toxoids combined with inactivated polio vaccine, when administered concomitantly with or as a diluent for a Hib conjugate vaccine

In an open trial. 400 infants were randomized to vaccination with a combined diphtheria-tetanus-pertussis-inactivated polio vaccine (DTaP-IPV) either mixed with a Haemophilits influenzae type b (Hib) tetanus toxoid conjugate immediately before injection (DTaP-IPV/Hib (mix)) or given concurrently with the Hib conjugate at separate injection sites (DTaP-IPV + Hib (sep)). The pertussis component consisted or pertussis toxoid alone. The vaccines were given intramuscularly at 3, 5 and 12 months of age. No vaccine-related serious adverse events occurred. Local reactions were evaluated from diary cards completed by the parents. Infants who received DTaP-IPV/Hib (mix) experienced fewer local reactions. Sera were obtained 28-45 days after the second and third vaccinations. Total Hib capsular antibodies were similar in the two groups after the second injection but lower in the group receiving DTaP-IPV/Hib (mix) than in the group receiving DTaP-IPV + Hib (sep) after the third injection (geometric mean 6.1 vs 10.4 mug/ml). Mixing of the vaccines also led to somewhat lower diphtheria toxin antibodies (5.9 vs 7.7 IU/ml after the third injection) while tetanus antibodies were higher (3.9 vs 2.5 IU/ml after the third injection). Antibodies against pertussis toxin and the three polio virus types were similar in the two groups. The moderate impairment of the Hib antibody response caused by mixing of the Hib conjugate with aluminium adsorbed DTaP may be due to physicochemical interference but is probably of little clinical importance because of the ability of the Hib conjugates to induce an immunologic memory. (C) 2001 Published by Elsevier Science Ltd.