Weinreich DM, Sivapalasingam S, Norton T, et al. - In the phase 1–2 portion of an adaptive trial, patients with coronavirus disease 2019 (Covid-19) exhibited reduction in the viral load and number of medical visits in correlation with receiving REGEN-COV, a combination of the monoclonal antibodies casirivimab and imdevimab. In vitro activity of REGEN-COV has been recorded against current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern. Findings from the phase 3 portion of this adaptive trial suggest that the risk of Covid-19–related hospitalization or death from any cause reduces when REGEN-COV is administered to the patients. Further, it results in more rapid resolution of symptoms and reduction in the SARS-CoV-2 viral load when compared with placebo.

• Outpatients with Covid-19 comprising cohort 1 (patients who were ≥18 years of age), cohort 2 (those who were <18 years of age), and cohort 3 (those who were pregnant at randomization) were involved in this phase 3 portion of the trial.

• Initially, the patients were administered intravenous REGEN-COV at a dose of 2,400 mg (1,200 mg each of casirivimab and imdevimab) or 8,000 mg (4,000 mg of each antibody) or intravenous placebo.

• REGEN-COV doses were linked with 4 days shorter median time to resolution of symptoms when compared with placebo.

• Efficacy of REGEN-COV was evident across various subgroups, including patients who were SARS-CoV-2 serum antibody–positive at baseline.

• Faster reduction in viral load occurred in participants receiving REGEN-COV doses vs placebo.

• The placebo group had a more frequent occurrence of serious adverse events (4.0%) than the 1,200-mg group (1.1%) and the 2,400-mg group (1.3%).