Do we need 3 doses of hepatitis B vaccine?

The hepatitis B virus (HBV) vaccine may provide protection through the clonal expansion of specific memory cells without necessarily having to produce high serum antibody levels. We develop a mathematical model which distinguishes between the accumulation of sensitive memory B and T-helper cells prior to a booster and the high circulating antibody levels present in an individual after a booster. We suggest this immune memory accumulates primarily in an antigen-independent fashion. These phenomena suggest individuals may be immune to infection six months after the priming vaccine dose(s) regardless of whether they receive a booster or not. This hypothesis is supported by immunogenicity data and by two independent vaccine efficacy trials comparing 0, 1 month schedules with 0, 1 and 6 month schedules.