To reduce the number of injections necessary to vaccinate young infants, various combined vaccines have been developed. The Comvax™ manufactured by Merck & Co. is a combination of Hepatitis B and PRP-OMP conjugate Haemophilus influenzae Type b vaccine. The purpose of this study is to evaluate the immunogenicity and safety of Comvax™ in Korean infants.

The infants who were vaccinated at 0 months of age with Hepatitis B vaccine, were recruited for this study after parental informed consent was obtained. The subjects were vaccinated with Comvax™ at 2 and 4 months of age. At each visit, infants were also immunized with DTaP, inactivated poliovirus vaccine, and pneumococcal vaccine when indicated. The serum anti-PRP and anti-HBs were measured at 2 months after the 1st dose(4 months age), and the 2nd dose(6 months age) by the ELISA and chemiluminescent microparticle immunoassay method, respectively. The local and systemic adverse reactions of vaccination were monitored for 3 consecutive days after each immunization.

Among sixty-five healthy infants(35 male infants) enrolled in this study; fifty eight(32 male infants) completed the scheduled immunizations. The geometric mean titers(GMTs) of anti-PRP at 2 months after the 1st dose and the 2nd dose were 1.96 µg/mL (95% CI; 1.38~2.78) and 10.02 µg/mL (95% CI; 7.04~14.26), respectively. Anti-PRP ≥1.0 µg/mL, was obtained in 63.2%(95% CI; 53.75~72.65) after 1 dose, and 96.6%(95% CI; 93.05~100) after 2 doses. The GMTs of anti-HBs were 38.32 mIU/mL(95% CI; 22.42~65.51), and 101.17 mIU/mL(95% CI; 65.94~155.25) at 2 month after the 1st dose and 2nd dose of Comvax™, respectively. Anti-HBs ≥10 mIU/mL was observed in 73.7%(95% CI; 65.07~82.33) after 1 dose and 94.8%(95% CI; 90.45~99.15) after 2 doses. Most of the adverse reactions after vaccination were mild. Irritability, the most common systemic reaction, was observed in 24.8%, followed by drowsiness(19.2%), poor feeding(19.2%) and fever(7.2%). Among the local reactions tenderness was observed in 25.6%, redness(≥ 5 mm) in 19.2% and swelling(≥5 mm) in 4.8%.

The Comvax™ vaccine was highly immunogenic for PRP and safe in Korean infants. Although the hepatitis B vaccine component was administered at 0, 2, 4 months, this study showed good immunogenicity against HBsAg.