New Data Show Combination Antibody Treatment Reduces Risk of Death in Hospitalized COVID-19 Patients


The RECOVERY study demonstrated that an antibody combination therapy (REGEN-COV; Regeneron) improved survival in hospitalized patients, a first for COVID-19 antibody treatments.


New data from the RECOVERY (Randomized Evaluation of COVid-19 thERapY) clinical trial indicated that the combination treatment with casirivimab and imdevimab (REGEN-COV; Regeneron Pharmaceuticals) significantly reduced the risk of death in patients who have been hospitalized with COVID-19.

Study investigators reported that casirivimab and imdevimab reduced the risk of death by 20% in hospitalized seronegative patients with COVID-19 – those who had not mounted a natural antibody response against SARS-CoV-2 – according to the news release.

The casirivimab-imdevimab combination has already been authorized by the FDA to treat nonhospitalized adult and pediatric patients with mild-to-moderate COVID-19 infection and who are at high risk for disease progression and death.

Related: FDA Adjusts EUA for COVID-19 Antibody Treatment

This news closely follows recent dosing changes that are now reflected in the emergency use authorization (EUA) granted to Regeneron; casirivimab and imdevimab dosages were both reduced to half in light of data showing that a 1200-mg dose (600 mg casirivimab and 600 mg imdevimab) was just as effective as a 2400-mg dose.

From September 2020 to May 2021, 9785 patients across 176 hospitals in the United Kingdom who had been hospitalized with COVID-19 were randomized to receive usual care plus 8000 mg intravenous (IV) infusion of the antibody combination or usual care alone. Investigators of the independently run clinical trial found that the antibody treatment reduced hospital stays by 4 days (13 days in the treatment group versus 17 days with usual care only). Analysis of seronegative patients demonstrated that 8000 mg of casirivimab plus imdevimab reduced all-cause mortality by 20% compared with usual care alone (24% of patients in the REGEN-COV group died versus 30% in the usual care group by day 28; rate ratio [RR]: 0.80; 95% confidence interval [CI]: 0.70-0.91; P=0.001).

Additionally, researchers reported that the proportion of patients discharged alive by day 28 was greater in the treatment group than the group receiving usual care (64% versus 58%; RR: 1.19; 95% CI: 1.08-1.30).

The UK-based clinical trial is the first to validate the potential for antibody treatments to improve survival rates in hospitalized COVID-19 patients. "Definitive phase 3 trials have now demonstrated that REGEN-COV can alter the course of COVID-19 infection, from prevention to very early infection, all the way through to when patients are on a ventilator in the hospital," said George D. Yancopoulos, MD, PhD, president and chief scientific officer at Regeneron.

Given the promising results, Regeneron intends to immediately update the FDA on the new findings and request that its EUA for the antibody treatment be expanded to include patients hospitalized with COVID-19. “We intend to rapidly discuss these results with regulatory authorities, including in the US where we will ask for our EUA to be expanded to include appropriate hospitalized patients,” Yancopoulos said.


  1. REGEN-COV (Casirivimab and imdevimab) Phase 3 Recovery Trial Meets Primary Outcome, Improving Survival in Hospitalized COVID-19 Patients Lacking An Immune Response to SARS-CoV-2. News Release. Regeneron; June 16, 2021. Accessed June 16, 2021.

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