Do we need 3 doses of hepatitis B vaccine?

The hepatitis B virus (HBV) vaccine may provide protection through the clon al expansion of specific memory cells without necessarily having to produce high serum antibody levels. We develop a mathematical model which distingu ishes between the accumulation of sensitive memory B and T-helper cells pri or to a booster and the high circulating antibody levels present in an indi vidual 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) regard less of whether they receive a booster or not. This hypothesis is supported by immunogenicity data and by two independent vaccine efficacy trials comp aring 0, 1 month schedules with 0, 1 and 6 month schedules. (C) 1999 Elsevi er Science Ltd. All rights reserved.