Persistence of specific antibodies after hepatitis B vaccination.

Antibody levels to hepatitis B surface antigen (anti-HBs) in healthy adults vaccinated with three doses of plasma-derived hepatitis B vaccine, containing 20, 10 or 5 micrograms of antigen, were followed for 4-6 years. After vaccination, 1034 of 1076 individuals had developed anti-HBs and 1016 had antibody concentrations above 10 IU/l. 681 of all initial responders could be tested after 1 year, 520 after 2, 380 after 3 and 213 after 4 years. 72 and 39 individuals, respectively, of the 185 earliest vaccinated volunteers were available for retesting after 5 and 6 years. Four years after the first vaccination, anti-HBs levels in 34% had dropped below 10 IU/l. The persistence of anti-HBs above this value depended on the peak antibody response after the third vaccination. Whereas all vaccinees tested with peak anti-HBs levels above 10,000 IU/l still had levels above 10 IU/l after 6 years, no-one with initial values between 10 and 100 IU/l maintained antibody concentrations above 10 IU/l for longer than 4 years. The rate of decrease in anti-HBs was independent of the peak anti-HBs value, the vaccine dose, and the age and sex of the vaccinees.