Half-life of HBs antibody after hepatitis B vaccination: an aid to timing of booster vaccination.

Antibody to hepatitis B virus surface antigen was measured in 48 paired sera from healthy medical staff who had been vaccinated against hepatitis B. The rate of antibody decline seemed unrelated to the height of the post-vaccination antibody titre and varied widely: even after correction for error of measurement, half-lives ranged from 40 to 280 days (mean 150, SD 52). For maintenance of protection, the recommended date for revaccination should be based on both the post-vaccination antibody level and the half-life, determined individually on completion of vaccination.