Lack of specific treatments for COVID-19 and the very time-consuming process of vaccine development lead us to trust traditional notions of immunization using passive transfer of humoral immunity. Passive immunization can be done using plasma therapy and IVIG therapy. Plasma from patients recovered from COVID-19 that contains antibodies against SARS-CoV2 has shown promising results in patients with severe COVID-19. Also, SARS-CoV and SARS-CoV2 are ideally similar in the structure and the cell entry receptor and protease. Studies show that serum from convalescent SARS patients and serum from rabbits immunized with SARS are both able to neutralize SARS-CoV2 efficiently. However, serum from bats immunized with SARS-lice coronavirus SL-CoV Rp3 could not exert such an effect. It is due to a noticeable degree of difference in the S1 domain in the S1 domain between the bat SL-CoV Rp3 strain and SARS-CoV2. A short-term moderate dose of IVIG combined with moderate-dose of corticosteroids might improve patient outcomes. Studies show that the viral RNA of SARS-CoV2 reaches its peak during the first week and then gradually decreases and that IgG and IgM begin to rise from the 10th day so that most patients have anti-viral antibodies by the 14th day. Passive immunization protects against disease, and so it should be administered as early as possible when the patient is diagnosed.