Which is the only serological marker present during window period in hepatitis B infection?

Following hepatitis B infection, HBsAg appear in the serum and is the first sign of infection. Antibodies to HBsAg i.e anti HBs occur after clearence of HBsAg. Window period refers to the time after the disappearence of HBsAg and appearence of anti HBs. During this window period, IgM anti HBc is positive. IgM anti HBc can persist for 3-6 months. HBeAg appear in the serum during the incubation period sholy after the detection of HBsAg. It indicates viral replication and infectivity.