A patient presented with features of acute hepatitis. He had a blood transfusion few weeks ago following an accident. Which of the following is the marker of the acute phase of hepatitis B infection?

In the acute phase of HBV infection, HBV surface antigen (HBsAg) and antibodies to HBV core antigen (anti-HBc) are detected in the serum. HBsAg disappears within 3-5 months, and antibodies to HBV surface antigen (HbsAb) do not appear until 6 months after infection. During this variable length "window period," anti-HBc antibody is the only serologic marker of infection. Immunity to HBV is conferred by anti-HBV surface antibodies (HBsAb) and is seen in resolved acute infection. Ref: Wyatt C., Butterwoh IV J.F., Moos P.J., Mackey D.C., Brown T.G. (2008). Chapter 15. Pathology of the Liver, Gallbladder, and Pancreas. In C. Wyatt, J.F. Butterwoh IV, P.J. Moos, D.C. Mackey, T.G. Brown (Eds), Pathology: The Big Picture.