Immune pressure exerted on HBV by anti-HBV antibodies and long-term therapy with drugs that mutagenize the viral P gene can select for mutations in its S gene, lead- ing to vaccine escape and evasion from serological detec-

Immune pressure exerted on HBV by anti-HBV antibodies and long-term therapy with drugs that mutagenize the viral P gene can select for mutations in its S gene, leading to vaccine escape and evasion from serological detection. Although transmissibility of these mutants is poor and their evolution towards heightened virulence appears slow, the situation could change as vaccination coverage increases, and treatment of patients with chronic hepatitis B and those coinfected by HIV and HBV becomes widespread. Enhanced surveillance programmes to track changes in the genotype and phenotype of the mutants are needed.