LONDON — Regulators in Britain granted approval to the experimental drug molnupiravir from U.S. pharmaceutical giant Merck on Thursday, marking the first authorization from a public health body for an oral antiviral treatment for COVID-19 in adults.

Experts have said that if widely authorized, the medicine could have huge potential to help fight the coronavirus pandemic: Pills are easier to take, manufacture and store, making them particularly useful in lower-to-middle-income countries with weaker infrastructure and limited vaccine supplies.

“We will continue to move with both rigor and urgency to bring molnupiravir to patients around the world as quickly as possible,” Merck President Robert Davis said in a statement.

The company, which added that it would submit applications to other regulatory agencies, has applied to the U.S. Food and Drug Administration for emergency-use authorization, while the European Medicines Agency has launched a rolling review of the drug.

“Today is a historic day for our country,” British Health Secretary Sajid Javid said in Thursday’s announcement. “This will be a game changer for the most vulnerable ... who will soon be able to receive the ground-breaking treatment.”

In a global clinical trial, the pill reduced hospitalizations and deaths by nearly half among higher-risk adult coronavirus patients diagnosed with mild to moderate illness, according to Merck, which developed the drug with Ridgeback Biotherapeutics after a discovery at Emory University. The first dose given to a volunteer in the trial was in the United Kingdom.

The U.K. medicines regulator approved the use of the treatment in people who are older than 60 or have at least one other factor that puts them at risk of covid-19 developing into severe illness, such as obesity and heart disease. The agency found it “safe and effective” at curbing the risk after “a rigorous review.”

Britain became known during the pandemic for its speed in authorizing vaccines. It was the first country in the world to approve a coronavirus vaccine tested in a large clinical trial when it granted emergency use authorization to the Pfizer-BioNTech shot last December.

Suerie Moon, co-director of the Global Health Center in Geneva, said the first approval of molnupiravir is “very significant in terms of giving patients and the public at large confidence that this treatment can be widely used.”

William Fischer, a pulmonary and critical-care physician and professor at the University of North Carolina at Chapel Hill, said the pill presents a chance to help overcome the inequities in access to treatment and prevention of the virus that have marked the pandemic. The pill is notably easy to use compared with monoclonal antibodies, a costly treatment that is infused or injected.

“Supply and the ability to provide these monoclonal antibodies is extraordinarily limited to really resource-rich countries,” said Fischer, who helped lead the Phase 2 clinical trial of molnupiravir.

He added, “This pill does play a really important role in terms of making sure that people have equal access to care.”

Virologists have said they are hopeful that as well as limiting the risk of developing severe illness, the treatment could help reduce transmission of the virus, too. And, since the pill can be picked up from a pharmacy and taken at home, Fischer said it will help prevent hospitals from becoming overwhelmed by COVID-19 patients and having to put off other types of care.

The United States has made an advance purchase of 1.7 million courses of molnupiravir at a cost of about $1.2 billion, or roughly $700 per treatment course. Other countries have also reached agreements with Merck to buy the pills, including Australia, Singapore and South Korea.

The U.S. drugmaker said that it expects to produce 10 million courses of the treatment by the end of this year, along with at least 20 million in 2022, and that it plans to adopt a “tiered pricing approach” taking into account each country’s ability to pay.

The firm has also agreed to share its license for the pill with several Indian manufacturers and with the Medicines Patent Pool, a U.N.-backed nonprofit organization, to allow production around the world and help boost access to more than 100 low- and middle-income countries. The move stood out in a pandemic that has seen pharmaceutical companies lobbying to keep rights to vaccines. More than 50 pharmaceutical companies from around the world have inquired about the molnupiravir license agreement, the Medicines Patent Pool said Thursday.

The U.K. approval marks “an important step,” Hervé Verhoosel, spokesman for Unitaid, a global health agency hosted by the World Health Organization, said in a statement.

“One of the most pressing challenges is now to guarantee a quality-assured generic market at lowest possible price and as rapidly as possible after relevant authorizations for all low- and middle-income countries,” Verhoosel said, adding that Unitaid and its partners are working to address potential market challenges in developing countries.

Advocacy organizations, however, have criticized Merck for leaving out upper-middle-income countries hit hard by the pandemic. Some are calling for the company to give up its patent for the drug.

“Pills are easier to manufacture and distribute in countries with insecure infrastructure so it’s vital that Merck releases the patent and trade secrets for this drug,” Tim Bierly, pharma campaigner at the U.K.-based organization Global Justice Now, said in a statement Thursday.

The drug — which received a type of conditional marketing authorization for products that fulfill an unmet medical need — will go by the name Lagevrio in Britain. It works by introducing errors that garble the genetic code of the virus and prevent it from making copies of itself. The window in which it can be administered and still work may be narrow, though, and the British regulator recommended taking it “as soon as possible” after a positive coronavirus test and within five days of symptoms onset.

The U.K. health secretary, Javid, called it “an excellent addition to our armory,” while urging people to keep getting their coronavirus shots. Doctors maintain the vaccines remain the principal tool against the coronavirus, as they seek to help prevent people from catching it rather than treating the disease after infection.