Persistence of antibody to hepatitis B surface antigen after low-dose, intradermal hepatitis B immunization and response to a booster dose

To determine the duration of antibody after low-dose, intradermal (i.d.), plasma-derived hepatitis B vaccination and the response to a booster dose, we studied two classes of medical students who were immunized with 2 μg doses i.d. In one class, 73 88 (85%) who had been immunized by skilled personnel at 0, 1 and 6 months, had protective concentrations (⩾ 10 mIU ml −1) of anti-HBs at 20 months after the first dose. Twelve (92%) out of 13 students who received only two doses at 0 and 1 months also had protective concentrations at month 20. At month 27, 11 16 (69%) with antibody ⩽10 mIU ml −1 responded to a fourth dose of 2 μg i.d. with protective concentrations of anti-HBs. In the second class, after three doses of vaccine at 0, 1, and 6 months, protective concentrations of anti-HBs were present in 90 93 (97%) at 14 months and in 71 80 (89%) at 25 months. In those who received only two doses, protective concentrations were found in 24 31 (74%) at 14 months and 9 16 (56%) at 25 months. After a booster dose of 2 μg i.d. at month 25, anti-HBs concentrations rose from a geometric mean of 78 to 1198 mIU ml −1 in 60 subjects previously immunized with three doses and from 18 to 1054 mIU ml −1 in 16 students previously immunized with only two doses. Overall, 73 76 (96%) of students in the second group had protective concentrations of antibody after the booster dose. Anti-HBs remains above protective concentrations after low-dose, i.d., plasma-derived hepatitis B vaccination in 85–89% of young adults when measured at 2 years after initial immunization. An i.d. booster dose at 2 years resulted in a sharp increase in anti-HBs regardless of whether the students had received two or three doses during initial immunization.