<prompt> A patient is found to be positive only for Anti HBsAg. All other viral markers are negative.The likely diagnosis is :VaccinationChronic hepatitis BAcute hepatitis BFulminant hepatitis B  <response>: Answer is A Vaccination Isolated Anti-HBs Ag in serum is seen in immunization with HB.s Ag. Possible Causes of Isolated Anti-HBsAg Positivity in serum Other markers negative Immunization with HBsAg after vaccination Hepatitis B in the remote past ? False-positive 