• David M Weinreich, Sumathi Sivapalasingam, Thomas Norton, Shazia Ali, Haitao Gao, Rafia Bhore, Jing Xiao, Andrea T Hooper, Jennifer D Hamilton, Bret J Musser, Diana Rofail, Mohamed Hussein, Joseph Im, Dominique Y Atmodjo, Christina Perry, Cynthia Pan, Adnan Mahmood, Romana Hosain, John D Davis, Kenneth C Turner, Alina Baum, Christos A Kyratsous, Yunji Kim, Amanda Cook, Wendy Kampman, Lilia Roque-Guerrero, Gerard Acloque, Hessam Aazami, Kevin Cannon, J Abraham Simón-Campos, Joseph A Bocchini, Bari Kowal, A Thomas DiCioccio, Yuhwen Soo, Gregory P Geba, Neil Stahl, Leah Lipsich, Ned Braunstein, Gary Herman, George D Yancopoulos, and Trial Investigators.
• From Regeneron Pharmaceuticals, Tarrytown (D.M.W., T.N., S.A., H.G., R.B., J.X., A.T.H., J.D.H., B.J.M., D.R., M.H., J.I., D.Y.A., C. Perry, C. Pan, A.M., R.H., J.D.D., K.C.T., A.B., C.A.K., Y.K., A.C., W.K., B.K., A.T.D., Y. S., G.P.G., N.S., L.L., N.B., G.H., G.D.Y.) and Excision BioTherapeutics, New York (S.S.) - both in New York; Bio-Medical Research (L.R.-G.) and Universal Medical and Research Center (G.A.) - both in Miami; Hope Clinical Research, Canoga Park, CA (H.A.); PMG Research of Wilmington, Wilmington, NC (K.C.); Köhler and Milstein Research, Hospital General Agustín O'Horan, Mérida, Mexico (J.A.S.-C.); and the Willis-Knighton Physician Network, Shreveport, LA (J.A.B).
• N. Engl. J. Med. 2021 Dec 2; 385 (23): e81e81.

BackgroundIn the phase 1-2 portion of an adaptive trial, REGEN-COV, a combination of the monoclonal antibodies casirivimab and imdevimab, reduced the viral load and number of medical visits in patients with coronavirus disease 2019 (Covid-19). REGEN-COV has activity in vitro against current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern.MethodsIn the phase 3 portion of an adaptive trial, we randomly assigned outpatients with Covid-19 and risk factors for severe disease to receive various doses of intravenous REGEN-COV or placebo. Patients were followed through day 29. A prespecified hierarchical analysis was used to assess the end points of hospitalization or death and the time to resolution of symptoms. Safety was also evaluated.ResultsCovid-19-related hospitalization or death from any cause occurred in 18 of 1355 patients in the REGEN-COV 2400-mg group (1.3%) and in 62 of 1341 patients in the placebo group who underwent randomization concurrently (4.6%) (relative risk reduction [1 minus the relative risk], 71.3%; P<0.001); these outcomes occurred in 7 of 736 patients in the REGEN-COV 1200-mg group (1.0%) and in 24 of 748 patients in the placebo group who underwent randomization concurrently (3.2%) (relative risk reduction, 70.4%; P = 0.002). The median time to resolution of symptoms was 4 days shorter with each REGEN-COV dose than with placebo (10 days vs. 14 days; P<0.001 for both comparisons). REGEN-COV was efficacious across various subgroups, including patients who were SARS-CoV-2 serum antibody-positive at baseline. Both REGEN-COV doses reduced viral load faster than placebo; the least-squares mean difference in viral load from baseline through day 7 was -0.71 log10 copies per milliliter (95% confidence interval [CI], -0.90 to -0.53) in the 1200-mg group and -0.86 log10 copies per milliliter (95% CI, -1.00 to -0.72) in the 2400-mg group. Serious adverse events occurred more frequently in the placebo group (4.0%) than in the 1200-mg group (1.1%) and the 2400-mg group (1.3%); infusion-related reactions of grade 2 or higher occurred in less than 0.3% of the patients in all groups.ConclusionsREGEN-COV reduced the risk of Covid-19-related hospitalization or death from any cause, and it resolved symptoms and reduced the SARS-CoV-2 viral load more rapidly than placebo. (Funded by Regeneron Pharmaceuticals and others; ClinicalTrials.gov number, NCT04425629.).Copyright © 2021 Massachusetts Medical Society.

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