Regeneron Pharmaceuticals Inc.’s antibody cocktail reduced the risk of death by 20% among hospitalized covid-19 patients who don’t have a natural antibody response of their own, according to a large study by University of Oxford researchers.

The results suggest there would be six fewer deaths over 28 days for every 100 patients given the company’s casirivimab and imdevimab combination of monoclonal antibodies. Patients who got the cocktail also spent four days fewer in the hospital on average, and had less of a need for a ventilator.

The combined therapy is already authorized in the U.S. for treating covid outpatients at risk of developing severe symptoms. The data reported Wednesday will be used to seek expanded emergency use for the drug cocktail for this large subset of hospitalized patients, Regeneron said in an email.

“This is a very important finding,” Fiona Watt, executive chair at the U.K.’s Medical Research Council, said in a statement. “It means that patients being hospitalized with covid-19 can be divided into two groups based on whether or not they have made antibodies to the virus.”

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There was no benefit, though, for roughly two thirds of the more than 9,700 patients studied who were either already producing covid antibodies or whose antibody status was unknown.


When a person is infected, their immune systems can generally produce natural antibodies to fight back against an invader. But some patients can’t manage to generate antibodies right away and end up severely sick. It’s a group that can include people whose immune systems have been damaged or suppressed.

“The trial was conducted at a time when most patients had not been fully vaccinated,” David Weinreich, Regeneron’s executive vice president for global clinical development, said in a statement. “These results provide hope to patients who have a poor immune response to either the vaccine or natural infection, as well as those who are exposed to variants for whom their existing antibodies might be suboptimal.”

Regeneron is partnered on the therapy with Roche Holding AG.

Testing for antibodies in coronavirus patients could become the norm, just as sick patients routinely get their blood pressure or oxygen levels checked, said Martin Landray, a study author and a professor of medicine and epidemiology at the University of Oxford.

“In the future it’s just one of the tests you run off to the laboratory,” Landray said at a news briefing. “It may not be a widespread practice immediately at the moment but I think it will be very rapidly because there’s a very strong use-case.”

The findings on Regeneron’s cocktail, part of the Recovery trial, come with the U.K. racing to vaccinate its population as the delta variant first detected in India spreads, and concerns mount over increased pressure on hospitals. The Regeneron cocktail is not currently authorized for use in the U.K..

The data will be reported Wednesday as a preprint article on medRxiv, and will be submitted moving forward to a medical journal, the authors said.

The University of Oxford’s Recovery trial has tested numerous other potential covid-19 drugs. Before this result, the trial is most famous for showing in a giant trial that the steroid dexamethasone could reduce the death rate for covid-19 patients on ventilators or needing supplemental oxygen. It’s now a standard treatment around the world.