Safety and immunogenicity of Haemophilus Influenzae type B vaccine given in combination with DTwP at 6, 10 and 14 weeks of age

Objective: To assess the immunogenicity and reactogenicity of a tetanus conjugate Haemophilus influenzae type b vaccine (Act-Hib™) when extemporaneously mixed and administered as a DTwP-Hib combination using an Indian DTwP vaccine (BE DTwP) in comparison with a licensed DTwP-Hib combination vaccine. Methods: 378 healthy infants were-enrolled and randomly allocated to receive either three doses, at 6, 10 and 14 weeks of age, of Act-Hib™ in combination with BE DTwP (Group A, n = 160), TetrAct-Hib™ (Group B, n = 160), or BE DTwP and Act-Hib™ as separate injections (Group C, n = 58). Sera collected before the first dose and one month after the third dose were tested for antibodies to vaccine antigens. Safety was determined using parental diary cards. Results: Anti-Hib antibody concentrations indicative of short-term protection (> 0.15 μg/ml) were elicited in all but one subject in Group A (99.3%), and all subjects in Groups B and C. The concentration of 1 μg/ml, considered to provide long-term protection, was achieved in 96.7%, 100% and 98.2% of the infants in Groups A, B and C, respectively. All children displayed satisfactory responses to the three DTwP component antigens, TetrAct-Hib eliciting higher titers against diphtheria and tetanus than BE DTwP. No vaccine-associated serious adverse events occurred. The BE DTwP vaccine was associated with more reports of fever than TetrAct-Hib, but most symptoms were regarded as mild and all resolved without sequelae. Conclusions: Combining Act-Hib™ and a local DTwP vaccine did not affect the anti-Hib response. In countries where DTwP vaccine available for use in the EPI program is manufactured by a local or other developing country manufacturer, mixing it with lyophilised Act-Hib™ is a reasonable option though the immunogenicity may have to be documented before routine use. However, use of TetrAct-Hib™ combination vaccine would be preferable in view of its lower reactogenicity and superior immunogenicity with respect to diphtheria and tetanus.