Hospital course summary and donor and patient plasma characterization. (A) Hospital course by clinical event, antiviral therapy (Tx), and C19-CP transfusion in relation to NP swab SARS-CoV-2 RNA results. Clinical events are as follows: acute respiratory failure on hospital day 12, staphylococcal scalded skin syndrome (SSSS) on hospital day 14, necrotizing enterococcus (NEC) on hospital day 23, intubation on hospital day 25, and extubation on hospital day 34. Dosages of antiviral therapy are as follows: remdesivir: 5 mg/kg per day on hospital day 15 and 2.5 mg/kg/day on hospital days 16 to 25; C19-CP donor 1: 10 mL/kg per day over 4 hours ∼20 hours apart on hospital days 28 and 29; and C19-CP donor 2: 10 mL/kg per day over 4 hours ∼20 hours apart on hospital days 31 and 32. (B) Enzyme-linked immunosorbent assays showing titration of samples from the 2 C19-CP donors and 3 negative controls collected before 2019, against SARS-CoV-2 spike RBD. End point titers were calculated using a cutoff of the average of the control samples, plus 3 times standard deviation value, marked with a dotted line. End points were calculated as the intersection of samples with this cutoff. Titers are shown numerically in the legend. (C) Neutralization activity of C19-CP donor samples against SARS-CoV-2. The focus reduction neutralization test (FRNT)₅₀ titers of the C19-CP donor samples were determined by an FRNT assay using an immunostain to detect infected foci. The dotted line represents the maximum concentrations of the serum tested (1/50). (D) Dynamics of RBD-specific end-point titers in the recipient after transfusion.