The decision tree model for premarriage prevention of HBV sexual transmission. Two similar intervention strategies start with HBsAg screening of all premarriage individuals. HBsAg negative individuals whose would-be spouse is HBsAg positive are considered for further intervention. Strategy 2 contains additional screening for HBcAb and applying the preventive protocol (P.P.) -see text- only to those negative for HBcAb (assumed to be serosusceptible) whereas in strategy 1, no HBcAb screening occurs and the prevention protocol (P.P.) is immediately performed. Only important probabilities are depicted in the figure. P1, P2, P3, P4 are defined in Table 1. P.P. stands for the preventive protocol explained in methods section in text.