Merck’s COVID-19 antiviral pill received its first approval in the United Kingdom on Thursday, with the U.K.’s medical regulator stating that the drug is “safe and effective at reducing the risk of hospitalization and death” in mild to moderate cases.

Sajid Javid, the British Health and Social Care Secretary, called the drug a “gamechanger.” The oral antiviral was developed by Merck and Ridgeback Biotherapeutics.

“Today is a watershed moment for our country, as the United Kingdom has become the first country in the world to approve a COVID-19 antiviral that can be taken at home,” Javid said.

The approval in the United Kingdom is based on clinical studies that showed the drug reduced the risk of hospitalization or death in at-risk adults with mild to moderate COVID-19 cases by about half.

The drug, known as molnupiravir and marketed in the United Kingdom as Lagevrio, aids people in coping with COVID-19 by interfering with the virus’ ability to replicate itself.

The Medicines and Healthcare Products Regulatory Agency, or MHRA, in the United Kingdom stated, “This prevents it from multiplying, keeping virus levels low in the body and thus reducing the severity of the disease.”

“Lagevrio is another therapeutic to add to our arsenal against COVID-19,” said Dr. June Raine, Chief Executive of the Medicines and Healthcare Products Regulatory Agency. “It’s also the first antiviral to be approved for this disease that can be taken orally rather than intravenously. This is significant because it means COVID-19 can be treated outside of a hospital setting before it progresses to a severe stage.”

Because of its ability to reduce viral levels in the body, the drug works best when taken as soon as possible after infection — ideally within five days of the onset of symptoms.

The drug has been approved by the Medicines and Healthcare Products Regulatory Agency (MHRA) for people with mild to moderate COVID-19 and at least one risk factor, such as obesity, heart disease, or being 60 or older.

According to Johns Hopkins University, COVID-19 rates are currently high in the United Kingdom, with 1.1 million cases reported in the last 28 days — the second-highest number in the world (after the United States).

According to the interim results of a large study released today, the prevalence of infection rose to 1.72 percent in late October, or about one in 58 people overall.

Molnupiravir is still being evaluated by the US Food and Drug Administration and the European Medicines Agency outside of the United Kingdom, according to Merck.