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Regeneron Pharmaceuticals said Monday that a single administration of its monoclonal antibody cocktail reduced the risk that volunteers exposed to Covid-19 would develop the disease by 81%.

The study enrolled 1,500 healthy volunteers, each of whom shared a home with someone who tested positive for SARS-CoV-2, and randomized them to receive a single dose of its antibody treatment, given subcutaneously as four shots, or placebo. After 29 days, 11 patients in the treatment group developed Covid-19 compared to 59 on placebo. And for the subjects who got Covid-19 despite treatment, their symptoms resolved after one week, compared to three weeks for those on placebo. In 204 patients who had already tested positive for the SARS-CoV-2 virus at the study’s outset, the injection reduced their chances of progressing to symptomatic Covid-19 by 31%.


The results were made public in a press release, and will be published in a scientific journal or presented at a medical meeting at a later date.

Those results mirror similar results seen in a study conducted by Eli Lilly of its monoclonal antibody in nursing homes. One key difference: While in previous studies by both Lilly and Regeneron, antibodies had to be given intravenously, in this one Regeneron used a formulation that could be given with an under-the-skin injection. Lilly is also exploring a subcutaneous injection of its antibodies.

That’s “a really, really big deal,” said Myron Cohen, director of the Institute for Global Health and Infectious Diseases at the University of North Carolina and one of the study’s lead investigators. He said that having to start an IV is “unequivocally” one of the barriers to using the antibodies either for treatment or prevention. The other barrier? Awareness.


“In order for these antibodies to be used for treatment and prevention and for treatment as prevention, we need the patients or their families familiar with the opportunity,” Cohen said. “We need health providers to be familiar with these drugs and comfortable administering them.”

And why do we need antibodies when there are already vaccines? Dan Barouch, the director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center and a key figure in the development of the J&J vaccine and another investigator in Regeneron’s study said that the approaches are “complementary.”

“As of now, there are still substantial numbers of people who are not fully vaccinated,” Barouch said. What’s more, some people, including those with compromised immune systems, might not generate enough antibodies one their own —– and could benefit from antibodies that are injected into their bodies.

In some circumstances, say, an outbreak at a nursing home, the monoclonal antibodies, which start working immediately, could be the better approach.

Adverse events occurred in 20% of those who received the antibody cocktail and 29% of those who received placebo. None of the antibody cocktail recipients were hospitalized, but four volunteers in the placebo group were. Injection site reactions occurred in 4% of those who received the antibody and 2% of those who received placebo.

Regeneron said 35% of study volunteers were Latinx and 5% were Black. About a third had at least one risk factor that would put them at high risk if they developed Covid-19. A third were obese, and 38% were over 50.

Correction: A previous version of this story misidentified Myron Cohen and the number of shots required.

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