Supplemental Digital Content is available in the text.

A significant proportion of patients infected with SARS‐CoV‐2 develop severe respiratory symptoms due to an excessive immune response. Treatment of this condition may include immunosuppressive therapies, such as IL‐6 receptor antagonists and corticosteroids, which poses a risk for patients with active or past hepatitis B virus (HBV) infection. In this prospective cohort study we analyzed the risk of HBV reactivation in patients with severe COVID‐19 and resolved HBV infection undergoing immunosuppressive therapy. From March 15 th to April 30 th 2020, 600 patients with severe COVID‐19 were admitted into our Hospital and treated with immune‐modulators. Data regarding HBV infection was available in 484, of whom 69 (14%) were HBsAg negative/anti‐HBc positive. For these patients, HBV reactivation prophylaxis with entecavir was strongly recommended. Complete follow‐up was available in 61 patients: 72% were male, median age was 67 years, and anti‐HBs was >10 IU/mL in 72%. The immunosuppressive drug most used was tocilizumab (72%). Despite HBV prophylaxis recommendation, 38 (62%) patients received entecavir and 23 (38%) did not. Baseline features of both groups were similar. At follow‐up, we found no cases of HBsAg seroreversion and only 2 (3%) patients (no prophylaxis group) had detectable serum HBV‐DNA (<15 IU/mL). Both were anti‐HBs negative and had normal aminotransferase levels. Our data show that the risk of HBV reactivation in patients with severe COVID‐19 and resolved HBV infection undergoing immunosuppressive treatment is low. However, if a systematic follow‐up after hospital discharge is unfeasible in patients without anti‐HBs, a short course of antiviral prophylaxis may be a safe option.