The use of Haemophilus influenzae type b-tetanus toxoid conjugate vaccine mixed with diphtheria-tetanus-pertussis vaccine in Gambian infants

Abstract

In preparation for an efficacy trial of PRP-T Haemophilus influenzae type b conjugate vaccine, 251 Gambian infants were randomized to receive three doses of PRP-T and diphtheria-tetanus-pertussis (DTP) vaccines at 2, 3 and 4 months of age, either by separate injections, or combined in the same syringe. One month after the third dose, there was no difference between anti-PRP levels in those infants who received the vaccines separately (GMT 5.83 μg ml −1), and those who received the vaccines combined (GMT 5.57 μg ml −1). The proportions achieving levels of 1.0 μg ml −1 were 89% and 92% in the “separate” and “combined” vaccine groups, respectively. There were no significant differences between groups in levels of antibody to diphtheria or tetanus. Geometric mean titres of antibody directed against pertussis antigens in the “separate” and “combined” groups were as follows: pertussis toxin 14.2 and 13.1 ELISA units (EU) ml −1; filamentous haemagglutinin 12.2 and 9.7 EU ml −1; pertactin 17.2 and 9.0 EU ml −1 ( P<0.05), fimbrial 2 3 antigens 449 and 364 EU ml −1. The combination of PRP-T and DTP in the syringe prior to administration is safe and immunogenic. The lower levels of anti-pertussis antibody are of unknown clinical significance.