Four kinds of Haemophilus influenzae type b protein conjugate vaccines, PRP-D, PRP-T, PRP-OMP and PRP-CRM197, have been developed, and PRP-T vaccines are currently produced by two manufacturer, ActHib® by Aventis and Hiberix™ by GlaxoSmith-Kline Biologicals. The purpose of this study is to evaluate the immunogenicity and safety of Hiberix™ in Korean infants.

Seventy-three healthy infants(43 male infants) were recruited for this study after parental informed consent was obtained. Each infant was vaccinated at 2, 4 and 6 months of age with the study vaccine. At each visit, infants were also immunized with DTaP, trivalent oral polio vaccine and hepatitis B vaccine when indicated. The serum anti-PRP antibody was measured at prevaccination, 2 month later after the 2nd dose, and 1 month later after the 3rd dose by the ELISA method. The local and systemic adverse reactions of vaccination were monitored for 3 consecutive days after each immunization. Immunogenicity of vaccine was evaluated in infants who received all the scheduled immunization and the adverse reactions were evaluated for infants who received at least one dose of the study vaccine.

Among seventy three infants, enrolled in this study; sixty three(37 male infants) completed all the scheduled immunizations. The geometric mean titer(GMT) of anti-PRP antibodies at prevaccination was 0.17 µg/mL(95% confidence interval[CI]; 0.13~0.22). The GMT of anti-PRP antibodies increased to 4.14 µg/mL(95% CI; 2.65~6.48) at 2 month later after the 2nd dose of PRP-T and 14.65 µg/mL(95% CI; 10.83~19.81) at 1 month later after the 3rd dose. Anti-PRP antibody ≥0.15 µg/mL, was observed in 98.4%(95% CI; 91.8~100) after 2 doses and 100%(95% CI; 100~100) after 3 doses. Anti-PRP antibody ≥1.0 µg/mL, was obtained in 77.8%(95% CI; 67.5~88.0) after 2 doses, and 98.4%(95% CI; 95.3~100) after 3 doses. Most of the adverse reaction after vaccination were mild. Irritability, the most common systemic reaction, was observed in 45.5%, followed by drowsiness(30.5%), poor feeding(26.7%) and fever(5.6%). Among the local reactions tenderness was observed in 7.9%, redness(≥5 mm) in 2.8% and swelling(≥5 mm) in 1.8%.

The PRP-T vaccine used in this study was highly immunogenic and safe in Korean young infants. The finding that high GMT and high frequency of infants with a protective titer achieved after 2 doses is consistent with the previous studies which were done with a PRP-T vaccine of other manufacturer. This study suggests that the immunization schedule of PRP-T vaccine for Korean infants may need re-evaluation.