Why is the research needed? The pandemic known as COVID-19 is now spreading across the world with currently (April 10, 2020) more than 1 115 530 active cases and 96 791 deaths. In most affected countries the current goal is to 'flatten the curve' of the epidemic since there is no health care system that is able to treat an extremely high volume of patients all at once. There is a need for immediately applicable treatments for the patients at highest risk, which gains time until targeted therapies become available. A key feature in the pathomechanism of the disease is that the virus elicits an immunological over-reaction in the human body termed 'cytokine storm'. In susceptible patients this hyper-inflammation itself is a significant burden and may even inhibit the body to generate antibodies against the virus in adequate quantities. Therefore, identifying the subset of patients with excess cytokine response and supplementing them with convalescent plasma from recovered donors may be a life-saving treatment option. What is our study about? In light of recent promising data on plasma therapy in the treatment of COVID-19 and other viral epidemics, there is a need for better understanding the cytokine response to the virus in order to better characterize the target population for convalescent plasma therapy. Our hypothesis is that convalescent plasma transfusion from healthy donors who recovered from SARS CoV-2 is able to reduce the cytokine storm in addition to replenish the patient's own antibodies in the acutely infected phase of the disease. A plasmapheresis donation of 400ml will be performed in subjects who recovered from COVID-19 and who are otherwise eligible for plasma donation. The sample will be tested for anti-SARS CoV-2 neutralizing antibody titers and those that reach the level of 1:320 will be processed for transfusion at the Hungarian National Transfusion Service. Recipients will be COVID-19 patients requiring hospitalization regardless of the severity of the disease or other co-morbidities. A blood-type matched transfusion of 200 ml convalescent plasma will be infused in a single sitting through an iv. infusion of 4 hours. Recipients will be followed up at days 1, 3,7,12, 17, 28 for clinical symptoms, antibody levels and cytokine response.