Statistical methods.
All derivations, statistical analyses, summaries, and listings were generated using SAS version 9.4 or higher (SAS Institute, Inc., Cary, North Carolina, United States). There were two analysis populations, the safety population and the PK population. The safety population included all randomized participants who received any amount of study treatment (COVID-HIGIV or placebo). All safety analyses were based on the safety population. The PK population included all randomized participants who received any amount of study treatment (COVID-HIGIV) according to the protocol and had an adequate set of evaluable PK samples (a suitable predose sample and at least one measurable postdose sample). A validated binding IgG immunoassay targeting anti-SARS-CoV-2 antibodies was used for the principal PK analyses. Serum concentration versus time data was analyzed by standard noncompartmental methods (i.e., linear trapezoidal method for consecutive time points with level or increasing concentrations and log-linear trapezoidal method for consecutive time points with decreasing concentrations) done manually using SAS software. Actual sample collection times and not nominal times were used in PK parameter estimates.