Blinding.
BLIND
Participants and investigators were unaware of treatment allocation in this study. Investigators enrolled participants. The pharmacy staff was provided unblinded access to the randomization assignment to prepare the study treatment. To maintain the blind, both the study drug and placebo had the same administration volume (400.0 mL), and study treatments were prepared in IV infusion bags that were covered with protective coverings to mask any differences between COVID-HIGIV and placebo appearance during IV infusion. Designated personnel at the sponsor’s bioanalytical laboratory assigned to perform PK sample testing were indirectly unblinded due to the nature of the test results, but measures were implemented not to disseminate this information until after database lock. The PK statistician remained blinded to subject COVID-HIGIV dose level throughout the study.Due to rapidly changing guidelines around the COVID-19 pandemic, a protocol amendment allowed participants to be unblinded in the study if they were eligible to receive the COVID-19 vaccine. Based on the Advisory Committee on Immunization Practices (ACIP) vaccination guidelines at the time, stating that those receiving passive immunotherapy should wait 90 days posttreatment to get vaccinated, only those that were in the placebo group were able to get vaccinated prior to study completion.