Abstract: Objective To analyze the immunological changes of severe COVID-19 patients after infusion of convalescent plasma. Methods Eight severe COVID-19 patients in our hospital were infused with COVID-19 convalescent plasma. The changes of IL-6, COVID-19 virus specific IgM and IgG antibodies, lymphocyte percentage and COVID-19 virus nucleic acid detection were compared before and after treatment. Adverse reactions of transfusion occurred during and after transfusion were recorded. Results On the first day after infusion, the percentage of lymphocytes in the patient decreased by 2.5%（P<0.01）. On the second day after infusion, the level of COVID-19 virus specific IgG increased by 6.04 AU/mL （P<0.05）. There was no significant change in specific IgM and lymphocyte percentage. One week after infusion, 62.5% of COVID-19 patients turned a negative nucleic acid test result. There was no significant change in IL-6 level before and after infusion. There were no blood transfusion adverse reactions. Conclusion Convalescent plasma may play a certain role in the treatment of patients with severe COVID-19.

Key words: Novel coronavirus pneumonia convalescent plasma, Patients with severe novel coronavirus pneumonia