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

SummaryObjectivesThe 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.MethodsImmune 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.ResultsOne 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.ConclusionA robust and protective Hib response was demonstrated following plain PRP and/or a booster conjugate Hib vaccine in both lower and higher Hib responders.