Inclusion Criteria:  PCR confirmed SARS-CoV-2 infection in a respiratory tract sample. Oxygen saturation (SaO2) of 94% or less while breathing ambient air or a ratio of the partial pressure of oxygen (PaO2) to the fraction of inspired oxygen (FiO2) of less than 300 mm Hg. High risk due to either pre-existing or concurrent hematological malignancy and/or active cancer therapy (incl. chemotherapy, radiotherapy, surgery) within the last 24 months or less (group 1) and/or chronic immunosuppression not meeting the criteria of group 1 (group 2) and/or Age ≥ 50 -75 years meeting neither the criteria of group 1 nor group 2 (group 3) and at least one of these criteria: Lymphopenia < 0.8 x G/l and/or D-dimer > 1μg/mL and/or Age ≥ 75 years meeting neither the criteria of group 1 nor group 2 (group 4). Blood hemoglobin concentration ≥ 8 g/dl. Provision of written informed consent. Patient is able to understand and comply with the protocol for the duration of the study, including treatment and scheduled visits and examinations. Male or female patient aged ≥ 18 years Postmenopausal or evidence of non-childbearing status. For women of childbearing potential: negative urine or serum pregnancy test within 14 days prior to study treatment.  Exclusion Criteria:  Dementia, psychiatric or cognitive illness or recreational drug/alcohol use that in the opinion of the principle investigator, would affect subject safety and/or compliance. Contraindication to transfusion or history of prior reactions to transfusion blood products. Patients with selective IgA deficiency. Patients with mechanical ventilation and/or extracoporal membrane oxygenation (ECMO) at time of initial inclusion into the trial. Mechanical ventilation is defined as either NIV - non-invasive ventilation or positive pressure ventilation. Enrollment into another clinical trial evaluating specific therapies for COVID-19 is encouraged. Participation in another trial with an investigational medicinal product. Treatment with SARS-CoV-2 convalescent/vaccine-boosted plasma in the past.