Britain’s regulator became the first in the world to approve Merck & Co.’s COVID-19 antiviral pill, describing the treatment as safe and effective following a swift review.

The drug, molnupiravir, was authorized for use in people with mild to moderate COVID-19 and at least one risk factor for developing severe illness, the U.K.’s Medicines and Healthcare Products Regulatory Agency said Thursday.

Boris Johnson’s government plans to focus on antiviral treatments while rolling out boosters to bolster immunity levels as winter approaches. The approval extends the U.K.’s record of quick action on COVID-19 clearances after it was the first western nation to give the go-ahead to Pfizer Inc. and BioNTech SE’s vaccine last year.

The U.K. has already announced deals to secure 480,000 courses of Merck’s pill. Based on the clinical trial data, Merck’s treatment is most effective when taken during the early stages of infection, the regulator said.

Molnupiravir has been hailed as a potential breakthrough, as it could be relatively cheap and easy to make, doesn’t require infusion and has shown it reduces the risk of hospitalization in a trial.