The predicted pattern of emergence of vaccine-resistant hepatitis B: a cause for concern?

We develop an epidemiological model of hepatitis B virus (HBV) in The Gambi a in order to investigate the possible patterns of emergence of a vaccine-r esistant strain. Under pessimistic assumptions (e.g., the current vaccine p rovides no cross-immunity against the variant) the model predicts the varia nt will not become dominant over the wild-type for at least 50 years. There fore the current low prevalence of variant infections is not evidence for h igh cross-immunity of the vaccine or for low infectiousness of the variant, but may simply be a consequence of the epidemiology of HBV. The efficacy o f the present vaccine against possible variants needs to be evaluated now t o determine whether vaccine modifications are required. However, the model also suggests that serological surveillance may be unable to determine this efficacy for 40-50 years. (C) 1999 Elsevier Science Ltd. All rights reserv ed.