The present invention relates to polymerase HBV mutant polypeptides comprising a mutated polymerase domain which is functionally disrupted for polymerase activity and fusion proteins comprising such polymerase mutant polypeptide. The present invention also relates to a nucleic acid molecule and an expression vector for expressing said polymerase mutant polypeptide as well as a composition which can be used for eliciting an immune response to HBV with the goal of providing a protective or therapeutic effect against HBV infection.