Regeneron's Antibody Cocktail Cuts Progression to Symptomatic COVID-19

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Regeneron Pharmaceuticals announced the results from its Phase III trial of recently infected asymptomatic COVID-19 patients for its REGEN-COV (casirivimab with imdevimab) antibody cocktail.

The therapy decreased the overall risk of the patients progressing to symptomatic COVID-19 by 31%, which was the trial's primary endpoint. It also decreased the overall risk of progression by 76% after the third day. In addition, REGEN-COV decreased the duration of symptoms and significantly reduced viral levels.

"COVID-19 transmission often occurs via infected people who do not yet have symptoms, so it is critical that we rapidly diagnose and treat these individuals for their own health and to prevent transmission," said Katharine Bar, co-principal investigator of the trial and assistant professor of medicine, infectious diseases, Hospital of the University of Pennsylvania. "These data pave the way for REGEN-COV to be used before patients become symptomatic, with a more convenient subcutaneous administration."

Regeneron also reported results from the second trial of REGEN-COV, which evaluated the combination therapy's ability to decrease the risk and burden of COVID-19 infection among household contacts of SARS-CoV-2 infected individuals. This was jointly run with the National Institute of Allergy and Infectious Diseases (NIAID).

The trial hit both primary and key secondary endpoints, demonstrating the antibody cocktail decreased the risk of symptomatic infections by 81% in people who were not infected when they began the trial. On average, people receiving the antibody therapy who had symptomatic infection resolved their symptoms in one week, compared to three weeks with placebo.

"These data suggest that REGEN-COV can complement widespread vaccination strategies, particularly for those at high risk of infection," said Myron Cohen, who heads the monoclonal antibody programs for the NIH-sponsored COVID Prevention Network (CoVPN) and is director of the Institute for Global Health & Infectious Diseases at the University of North Carolina at Chapel Hill. "Despite standard precautions to reduce transmission, nearly 10% of unvaccinated individuals living with an infected person developed symptomatic infections if they did not receive REGEN-COV. If authorized, convenient subcutaneous administration of REGEN-COV could help control outbreaks in high-risk settings where individuals have not yet been vaccinated, including individual households and group living settings."

In the first trial, adverse events (AE) occurred in 34% of patients receiving REGEN-COV and 48% of placebo patients, with serious adverse events occurring in 0% of the REGEN-COV cohort and 3% of the placebo patients. No patients dropped out of the test from AEs, and there were no deaths.

In the second trial, adverse events occurred in 20% of patients receiving REGEN-COV and 29% in the placebo group, with serious adverse events in 1% of the REGEN-COV cohort and 1% in the placebo group. Zero REGEN-COV participants were either hospitalized or visited the emergency room because of COVID-19 during the 29-day efficacy assessment period, while four in the placebo group did. None withdrew from the trial from adverse events, and none of the deaths in the trial—two in the antibody group and two in the placebo group, were related to COVID-19 or the study drug.

REGEN-COV is still being studied in clinical trials in multiple settings. These include for prevention of COVID-19 in households contacts of infected people; in non-hospitalized and certain hospitalized patients, including the open-label RECOVERY trial of hospitalized patients being run in the U.K.

"With more than 60,000 Americans continuing to be diagnosed with COVID-19 every day, the REGEN-COV antibody cocktail may help provide immediate protection to unvaccinated people who are exposed to the virus, and we are also working to understand its potential to provide ongoing protection for immunocompromised patients who may not respond well to vaccines," George D. Yancopoulos, president and chief scientific officer of Regeneron, said. "We thank the individuals, investigators and our collaborators involved in the trial, and look forward to rapidly discussing these results with regulatory authorities."

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