Early Data Show Regeneron Cocktail Prevents Symptomatic COVID-19 Infection

REGEN-COV consists of 2 potent, virus-neutralizing antibodies that bind noncompetitively to the receptor binding domain of the SARS-CoV-2 spike protein.

Positive results were announced from an ongoing phase 3 trial of REGEN-COV (casirivimab and imdevimab; Regeneron) used as a passive vaccine for the prevention of coronavirus disease 2019 (COVID-19) in individuals at high risk of infection due to a household exposure to a COVID-19 patient.

REGEN-COV consists of 2 potent, virus-neutralizing antibodies that bind noncompetitively to the receptor binding domain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, thereby blocking its interaction with the host cell. This is believed to decrease the ability of mutant viruses to escape treatment and protect against spike variants.

The trial, which is being conducted in collaboration with the National Institute of Allergy and Infectious Diseases, is evaluating the use of REGEN-COV for immediate short-term passive immunity to prevent SARS-CoV-2 infection. Participants were randomly assigned to receive either REGEN-COV subcutaneously or placebo.

Interim findings showed that passive vaccination with REGEN-COV resulted in 100% prevention of symptomatic infection (n=0/186) compared with placebo (n=8/223) and approximately 50% lower overall rates of infection (n=10/186 vs n=23/223 for placebo, respectively). Infections that occurred in the REGEN-COV arm were all asymptomatic, with decreased peak virus levels and short duration of viral shedding; these infections lasted no more than 1 week, while approximately 40% of infections in the placebo arm lasted 3 to 4 weeks.

REGEN-COV was also associated with lower disease burden, which included fewer total viral shedding weeks (9 weeks vs 44 weeks for placebo), fewer total high viral shedding weeks (0 weeks vs 22 weeks for placebo), and fewer total symptomatic weeks (0 weeks vs 18 weeks for placebo).

As for safety, REGEN-COV was associated with fewer adverse events compared with placebo (12% vs 18%, respectively). There were no deaths or COVID-19 hospitalizations in the REGEN-COV arm and 1 death and 1 COVID-19-related hospitalization in the placebo arm. 

“These data using REGEN-COV as a passive vaccine suggest that it may both reduce transmission of the virus as well as reduce viral and disease burden in those who still get infected,” said George D. Yancopoulos, MD, PhD, President and Chief Scientific Officer at Regeneron. “There are also many individuals who unfortunately may be immunocompromised and not respond well to an active vaccine or are otherwise unable to be vaccinated, and REGEN-COV has the potential to be an important option for these individuals.”

In November 2020, the Food and Drug Administration granted REGEN-COV Emergency Use Authorization for the treatment of mild to moderate COVID-19 in adults and pediatric patients aged 12 years and older weighing at least 40kg, who have received positive results of direct SARS-CoV-2 viral testing and are at high risk for progressing to severe COVID-19.

“In this prevention trial, REGEN-COV was given as injections rather than an infusion, which makes administration much more convenient and efficient for patients and overburdened health care providers and facilities,” said David Weinreich, MD, Executive Vice President and Head of Global Clinical Development at Regeneron. “We look forward to seeing the full dataset early next quarter and will discuss the current results with regulatory authorities, including the potential to expand the Emergency Use Authorization.”


Regeneron reports positive interim data with REGEN-COV™ antibody cocktail used as passive vaccine to prevent COVID-19. [press release]. Tarrytown, NY: Regeneron Pharmaceuticals, Inc; January 26, 2021. 

This article originally appeared on MPR