VACCINE-INDUCED IMMUNOLOGICAL MEMORY FOR HEPATITIS-B SURFACE-ANTIGEN - IMPLICATIONS FOR POLICY ON BOOSTER VACCINATION

This paper reviews published literature on the long-term persistence o f immunologic memory for HBsAg after a course of hepatitis B vaccine a nd the functional significance this has for policy on booster vaccinat ion. Several studies have shown that vaccine induced antibody (anti-HB s) specific for the surface antigen (HBsAg) of hepatitis B virus (HBV) is protective at a serum concentration of 10 milli-International Unit s per milliliter (mIU ml(-1)). When acquired passively (e.g. from hepa titis B immune globulin), susceptibility to infection returns as antib ody declines. However, vaccine induces active synthesis of anti-HBs ac companied by immunologic memory for HBsAg that affords ongoing protect ion independent of antibody. Persistent memory over periods of 5 years or more is evident from large, rapid increases in antibody following booster vaccination, even in subjects who have lost antibody. Compleme ntary studies, using an in vitro enzyme linked immunosorbent assay (sp ot-ELISA), show that the number of memory B lymphocytes able to produc e anti-HBs does not diminish as the level of antibody declines. That i mmunologic memory provides effective immunity is suggested by serologi c studies over periods of 5 years or more of vaccinees frequently expo sed to HBV. Although many failed to maintain at least 10 mIU ml(-1) of antibody, there have been very few clinically significant breakthroug h infections. Thus, it appears unnecessary to give healthy vaccinees a booster vaccination when the level of anti-HBs fall below 10 mIU ml(- 1). Current studies suggest good retention of immunologic memory in he althy vaccinees over periods of 5-12 years. While additional studies w ill better define the limits of this phenomenon, routine booster vacci nation should not be needed to sustain immunologic memory and protecti on within 5 years and perhaps longer after the primary vaccination ser ies. Copyright (C) 1996 Elsevier Science Ltd.