Regeneron Pharmaceuticals Inc. said data from a late-stage clinical trial suggest that its antibody cocktail therapy for COVID-19 significantly reduces virus levels and the need for further medical care.

Patients getting the therapy were 57 per cent less likely to need medical care within a month of treatment, with 2.8% of those given the antibody and 6.5 per cent of those on placebo seeing a health-care worker within 29 days.

The Tarrytown, New York-based company has shared the results with U.S. regulators who are currently evaluated the antibody cocktail for an emergency use authorization for high risk patients with mild-to-moderate COVID-19. Regeneron’s therapy was given to President Donald Trump earlier this month after he tested positive for the coronavirus.

Shares of Regeneron rose 3 per cent in after-hours trading in New York on Wednesday.

“We continue to see the strongest effects in patients who are most at risk for poor outcomes due to high viral load,” said Chief Scientific Officer George Yancopoloulos.

Since the therapy had similar benefit at the high and low doses, Regeneron is considering a change to the dosing it’s using in other outpatient studies that are underway. The change to a lower dose could help extend the limited available supply of the medication.

The treatment appeared to be the most potent for those at higher risk, including older patients and those with other medical conditions including obesity, heart, lung, liver or kidney disease, the company said. Patients who had the highest viral levels, or produced the lowest levels of antibodies themselves, were most likely to respond to treatment.

Regeneron’s treatment, called REGN-COV2, consists of two monoclonal antibodies against the coronavirus spike protein. It is considered one of the most promising potential coronavirus treatments being studied. Preliminary results from a clinical trial that Regeneron released in September showed the drug may help treat coronavirus patients outside of the hospital by reducing virus levels and symptoms, the company said.

Experimental antibody therapies could become a powerful component of the arsenal that doctors use to treat patients who’ve contracted coronavirus. Anthony Fauci, the top U.S. infectious-disease official, has referred to antibody-based medicines that could treat infected patients soon after they contract the virus as a bridge to a vaccine.

Antibody therapies also are being studied in the hospital setting to treat those with more severe cases, and as short-term treatments that could be given to people such as nursing home residents or staff who may have been exposed during a local outbreak to prevent them from getting sick.

Other companies testing antibody treatments include Eli Lilly & Co., AstraZeneca Plc and GlaxoSmithKline Plc and its partner Vir Biotechnology Inc.