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November 4, 2021

Written by Sam Parnell

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Use of REGEN-COV, a combination of the monoclonal antibodies casirivimab and imdevimab, for patients with Covid-19 infection was associated with faster symptom resolution and reduced risk of hospitalization or death compared to placebo.

Why does this matter?
The Covid-19 pandemic has sickened more than 240 million people and has resulted in almost 5 million deaths. Although most individuals infected with SARS-CoV-2 only have mild to moderate disease, some patients develop severe infection that can lead to hospitalization and death. We know that dexamethasone is helpful for patients with severe COVID-19 disease who require respiratory support, but are there any evidence-based treatment options for the vast majority of patients with only mild to moderate disease?

Monoclonal antibodies for the win!

Design: This was the phase 3 portion of an adaptive trial of outpatient individuals with Covid-19 infection and risk factors for severe disease who were randomized to receive various doses of REGEN-COV or placebo (normal saline). Patients were enrolled between September 24, 2020 and January 17, 2021 and were followed through day 29.

Results: Covid-19 related hospitalization or death occurred in 1.3% of patients in the REGEN-COV 2400-mg group compared to 4.6% of patients in the concurrent placebo group (relative risk reduction, 71.3%; P<0.001) and in 1.0% of patients in the REGEN-COV 1200-mg group compared to 3.2% of patients in the concurrent placebo group (relative risk reduction, 70.4%; P=0.002). Median time to symptom resolution was 4 days shorter for each REGEN-COV dose group compared to placebo (10 days vs 14 days; P<0.001). REGEN-COV was efficacious across various subgroups, including patients who were SARS-CoV-2 serum antibody-positive at baseline. All REGEN-COV dose levels were associated with more rapid declines in viral load.

Adverse events were rare and more common in the placebo group (4.0%) than the REGEN-COV groups (1.1% 1200-mg group, 1.3% 2400-mg group). Less than 0.3% of patients had grade 2 or higher infusion-related reactions.

Implications: This data supports the use of REGEN-COV treatment for patients with Covid-19 who are at high risk of severe disease. REGEN-COV leads to reduced risk of Covid-19 hospitalization or death, allows for faster symptom resolution, and has been listed in the NIH treatment guidelines for high-risk outpatients with Covid-19.

Limitations: The study was funded by Regeneron Pharmaceuticals and was not powered to find a difference in mortality. Overall, only 5 deaths occurred (2 in the REGEN-COV groups and 3 in the placebo groups). In addition, this data was collected before the Delta variant was the dominant strain (although in vitro studies have shown REGEN-COV has efficacy against circulating variants of concern including the alpha, beta, delta, and gamma variants).

REGEN-COV Antibody Combination and Outcomes in Outpatients with Covid-19. N Engl J Med. 2021 Sep 29;NEJMoa2108163. doi: 10.1056/NEJMoa2108163. Online ahead of print.

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