If cleared, Merck’s drug would be the first pill shown to treat COVID-19, a potentially major advance in efforts to fight the pandemic. All COVID-19 therapies now authorized in the U.S. require an IV or injection.

Merck and its partner Ridgeback Biotherapeutics said early results showed patients who received the drug, called molnupiravir, within five days of COVID-19 symptoms had about half the rate of hospitalization and death as patients who received a dummy pill. The study tracked 775 adults with mild-to-moderate COVID-19 who were considered higher risk for severe disease due to health problems such as obesity, diabetes or heart disease.

Among patients taking molnupiravir, 7.3% were either hospitalized or died at the end of 30 days, compared with 14.1% of those getting the dummy pill. There were no deaths in the drug group after that time period compared with eight deaths in the placebo group, according to Merck. The results were released by the company and have not been peer reviewed. Merck said it plans to present them at a future medical meeting.

An independent group of medical experts monitoring the trial recommended stopping it early because the interim results were so strong. Company executives said they are in discussions with the Food and Drug Administration and plan submit the data for review in coming days.

“It exceeded what I thought the drug might be able to do in this clinical trial,” said Dr. Dean Li, vice president of Merck research. “When you see a 50% reduction in hospitalization or death that’s a substantial clinical impact.”

Side effects were reported by both groups in the Merck trial, but they were slightly more common among the group that received a dummy pill. The company did not specify the problems.

Earlier study results showed the drug did not benefit patients who were already hospitalized with severe disease.

The U.S. has approved one antiviral drug, remdesivir, specifically for COVID-19, and allowed emergency use of three antibody therapies that help the immune system fight the virus. But all the drugs have to given by IV or injection at hospitals or medical clinics, and supplies have been stretched by the latest surge of the delta variant.

Health experts including the top U.S. infectious disease expert Dr. Anthony Fauci have long called for a convenient pill that patients could take when COVID-19 symptoms first appear, much the way the decades-old flu medication Tamiflu helps fight influenza. Such medications are seen as key to controlling future waves of infection and reducing the impact of the pandemic.

Merck’s pill works by interfering with an enzyme the coronavirus uses to copy its genetic code and reproduce itself. It has shown similar activity against other viruses.

The U.S. government has committed to purchase 1.7 million doses of the drug if it is authorized by the FDA. Merck has said it can produce 10 million doses by the end of the year and has contracts with governments worldwide. The company has not announced prices.

Several other companies, including Pfizer and Roche, are studying similar drugs that could report results in the coming weeks and months.

Merck had planned to enroll more than 1,500 patients in its late-stage trial before the independent board stopped it early. The results reported Friday included patients enrolled across Latin America, Europe and Africa. Executives estimated about 10% of patients studied were from the U.S.

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