disclosed are live hepatitis a virus deletion mutants having a deletion mutation in the 5 &# 39 ; nontranslated region of the viral genome . the deletion mutation may be selected from the group consisting of py1 deletion mutations that cause the virus to retain the ability to replicate in monkey kidney cells ; and deletion mutations between nucleotides 140 and 144 that render the virus temperature sensitive . advantageously , the deletion mutation may be an attenuating mutation . pharmaceutical formulations containing such viruses are disclosed , along with the use thereof to produce antibodies useful for diagnostic purposes and for imparting protective immunity against hepatitis a virus .