Regeneron says its Covid-19 antibody cocktail helps prevent symptomatic Covid-19

New Phase 3 trial data finds a single shot of Regeneron’s Covid-19 antibody cocktail was able to prevent symptomatic Covid-19 among people exposed to the virus, the company said Monday.

Regeneron said it will seek expansion of the emergency use authorization for the drug, which is currently available in the United States to treat mild-to-moderate Covid-19 in people already infected with the coronavirus.

In the new trial, the drug, named REGEN-COV, reduced risk of symptomatic infections by 81%, the company said Monday in a news release. The trial studied Regeneron’s combination of casirivimab with imdevimab in 1,505 people who had not been infected with coronavirus but lived in the same household as someone who tested positive in the four days before. Each participant received one dose of the drug or a placebo, which does nothing, administered as an injection through the skin.

After 29 days, 11 people who received a single 1,200 mg dose of the treatment developed symptomatic Covid-19; 59 people who received a placebo developed symptomatic Covid-19. The drug provided 72% protection against symptomatic infections in the first week and 93% protection in subsequent weeks, Regeneron said. The data has not yet been peer reviewed or published.

Those who received the antibody cocktail and experienced a symptomatic infection resolved their symptoms in one week, the company said, compared to three weeks among those who received a placebo.

“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,” Dr. Myron Cohen, who leads the monoclonal antibody efforts for the COVID Prevention Network and is the director of the Institute for Global Health and Infectious Diseases at the University of North Carolina at Chapel Hill, said in a statement. “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.”

Adverse events occurred in 20% of patients who received the antibody drug and 29% of those who received a placebo, Regeneron said. None of the participants who received the drug were hospitalized or went to the ER because of Covid-19 over the course of 29 days; four in the placebo group did so. None of the four deaths in the trial — two among those who received the drug and two who received a placebo — were due to Covid-19 or the drug.

Regeneron said it will request an expansion of its US Food and Drug Administration emergency use authorization to include Covid-19 prevention and as a subcutaneous shot. The drug is currently authorized to be administered as an IV, which takes longer and may be part of the reason why uptake of the treatment has been limited.

The company also announced Monday that a second Phase 3 trial studied an injection of its antibody cocktail in 204 asymptomatic people recently infected with the coronavirus. A single shot reduced the risk of progressing to symptomatic Covid-19 by 31% overall. After the third day, risk was reduced by 76%. Participants received the treatment or a placebo, and the trial showed that the duration of symptoms was shortened and viral levels were reduced in those who received the antibody cocktail.

Eli Lilly and Company previously announced its monoclonal antibody therapy, bamlanivimab, helped prevent symptomatic Covid-19 infection among nursing home residents and staff. However, the US government said last month it will no longer distribute bamlanivimab for use on its own because of a sustained increase in coronavirus variants in the United States. Bamlanivimab can still be used with etesevimab, another monoclonal antibody treatment developed by Eli Lilly; in combination, the two Eli Lilly treatments seem to work against coronavirus variants.

So far, Regeneron’s cocktail has been shown to be effective against coronavirus variants of concerns.