Primary and booster immunization with a diphtheria, tetanus, acellular pertussis, hepatitis B (DTPa-HBV) and Haemophilus influenzae type b (Hib) vaccine administered separately or together is safe and immunogenic

Abstract

Objectives: The aim of this study was to evaluate the safety and immunogenicity of DTPa–HBV and Hib vaccines given mixed or separately to 360 healthy infants at 2, 4, and 6 months of age. Methods: Immune memory was assessed in lower responders (post-primary anti-PRP <0.545 μg/ml), through administration of plain polyribosylribitol phosphate (PRP) at 12–15 months. All subjects received a DTPa–HBV/Hib booster at 18–19 months. Results: One month after primary vaccination, 98% had seroprotective antibody levels against HBV and 94–97% against Hib (anti-PRP ≥ 0.15 μg/ml). A statistically significant difference between groups was observed in the proportion of subjects who achieved anti-PRP antibodies ≥1.0 μg/ml post-primary vaccination; 68.1% for DTPa–HBV/Hib and 84.5% for DTPa–HBV and Hib. PRP administered to lower responders produced a 7-fold increase in anti-PRP antibodies, indicative of immunological memory. After DTPa–HBV/Hib booster vaccination, 96–100% of subjects had seroprotective antibody concentrations against Hib, hepatitis B, tetanus, and diphtheria and high vaccine response rates against pertussis toxoid, filamentous hemagglutinin, and pertactin. Conclusion: A robust and protective Hib response was demonstrated following plain PRP and/or a booster conjugate Hib vaccine in both lower and higher Hib responders.