In Case 2, the patient showed lymphopenia from day 1, and it persisted even after clinical improvement with corticosteroid use. When the convalescent plasma was administered on day 6, lymphocyte count immediately rose to normal level (from 0.52 × 103/µL to 1.21 × 103/µL) and then remained in the normal range. Patients with severe COVID-19 pneumonia and ARDS also presented with lymphopenia in other studies.11 Some authors hypothesized that continuous and gradual increases in lymphocyte count might be required for immunity against SARS-CoV-2 infection.11 In SARS patients, lymphopenia existed at the onset of illness and persisted until the recovery period.1819 These findings were consistent with the recovery of lymphocyte count with clinical improvement of Case 2 after the use of convalescent plasma.