Decreased expression of HBV surface antigen (HBsAg) with sK122R and sV96A co-mutation is associated with an ineffective antibody response in a chronic hepatitis B patient

•Two mutation sites sV96A and sK122R were identified from a CHB patients demonstrated abnormal serum markers. This is a new double mutation site and has not been reported previously.•The levels of HBsAg with amino acid substitutions sV96A-sK122R were greatly reduced in culture supernatants but were apparently increased in the intracellular fraction.•HBsAg neutralization by HBsAb in this patient may have been compromised by the HBsAg sK122R amino acid substitution, suggesting that antibodies produced by the patient had lost their HBV-neutralizing effect. This is the cause of hepatitis B virus immune escape in patients.