To date, apart from supportive care, no specific treatment has been proven to be effective for SARS-CoV-2 infection. To that end, currently, there is a large number of studies to investigate therapies for COVID-19, including convalescent plasma (CP) from recovered COVID-19 patients as treatment. Clinical trials are underway to investigate the efficacy of CP transfusion, new antiviral drugs and vaccines. Although CP has not always proven to be an effective therapy as proven for Ebola virus disease, CP therapy is marked by a success story. Why does this happen? Although some studies have been published or are still in progress, we propose a careful evaluation of the dosage of the therapy, here referred to as 'therapeutic unit'. The amount of neutralizing antibodies and the period of their administration may determine whether such passive immunotherapy in patients at high risk of deleterious evolution may reduce the frequency of patient deterioration, and thereby mortality.