Studies of immune response to hepatitis B vaccine in Thai blood donors

The immunogenicity of heat-inactivated plasma derived hepatitis B vaccines were studied in one hundred and eighty-two adult blood donor volunteers whose HBV markers (HBsAg, anti-HBs) were negative. They were randomized for four regimens of 3 micrograms intramuscular Hepaccine-B vaccine at the schedules of 0, 1, 2, 9 months, 0, 1, 3, 9 months, 0, 2, 6, 12 months, 0, 1, 6, 12 months and another regimen of 5 micrograms Hevac-B Pasteur vaccine at 0, 1, 2, 9 months. Blood specimens, tested for serological marker (anti-HBs), were drawn at 1, 3, 6, 9, 12 and 15 months following the initial injection. The outcome revealed that the Hepaccine-B vaccinated group in the schedules of 0, 2, 6, 12 and 0, 1, 6, 12 months yielded seroconversion rates of 48.7% and 56.8%, respectively one month after vaccination. After that, the immune response (anti-HBs titer) regularly increased every three months until it reached 100% with a geometric mean (GMT) of 135 and 130 mIU/ml respectively in the fifteenth month. Taking the Hepaccine-B and the Hevac-B Pasteur with the same schedule (0, 1, 2, 9 months) into consideration, we found that the former yielded the higher seroconversion rate, one month after the initial injection, which increased to the highest rate of 95.8% in the ninth month. After that it was steady until the fifteenth month with higher GMT (584 mIU/ml) than that of Hevac-B Pasteur (323 mIU/ml). The seroconversion rate of Hevac-B Pasteur in the first month was lower than that of Hepaccine-B but it yielded the highest rate of 100% in the sixth month. After that, it gradually decreased and again increased to 100% in the fifteenth month.