Merck’s molnupiravir pills. Clinical trial data has suggested that the drug is most effective when taken during the early stages of infection. Credit...Via Reuters

Britain on Thursday became the first country to authorize the use of an antiviral pill for Covid-19, an easy-to-use treatment that could help tame the pandemic.

The drug, known as molnupiravir and sold by the pharmaceutical company Merck, was shown in a key clinical trial to reduce by halfthe risk of hospitalization and death in high-risk Covid patients who were treated early in their infections. Dispensed from a pharmacy and taken at home, the drug is expected to reach many more people than treatments like monoclonal antibodies, which are typically administered intravenously at a hospital or clinic.

Britain, which has already ordered enough supplies of the pill for 480,000 people, is one of growing list of wealthy countries that have raced to lock up supplies of the drug. Merck said last week it has reached deals to sell the pills to the governments of the United States, Australia, South Korea, New Zealand, Serbia and Singapore.

The drug is expected to become available in the United States as soon as December, after a panel of experts meets at the end of this month to make a recommendation to the Food and Drug Administration about whether it should be authorized for high-risk Covid patients. The United States has ordered enough supply of the drug for 1.7 million patients, at a cost of about $700 per person.

Britain’s regulator, the Medicines and Healthcare products Regulatory Agency, recommended giving the drug to people as soon as possible after a positive coronavirus test and within five days of the onset of symptoms. The full course of treatment is 40 pills over five days.

The regulator authorized the drug for both vaccinated and unvaccinated people who have at least one trait — such as being over 60 years old or having obesity — that would put them at high risk for becoming severely ill from the virus.

Britain is logging an average of nearly 40,000 virus cases daily, though it has recently seen a slight decline in the number of positive cases.

So far, 75 percent of Britain’s population has received at least one dose of a coronavirus vaccine, while 68 percent have been fully vaccinated, according to a New York Times database.

Sajid Javid, the British health secretary, described the Merck pill’s authorization as a “historic day” for the country. “This will be a game changer for the most vulnerable and the immunosuppressed, who will soon be able to receive the groundbreaking treatment,” he said.