Paxlovid, made by Pfizer, reduced the risk of severe disease by nearly 90% in clinical trials and appeared to be safe. Taken as a pill soon after COVID-19 symptoms start, it is intended for people at high risk for severe disease, including those over 65, people with obesity or diabetes and anyone with a weakened immune system, as well as high-risk children ages 12 and up.

On Wednesday, White House COVID-19 response coordinator Jeff Zients said the U.S. government has purchased 10 million treatment courses of Paxlovid, with 265,000 set to be available to Americans in January. The pills take 6-8 months to produce, according to Pfizer.

"The Pfizer team has very promising and now authorized treatment. A pill that dramatically reduces the risk of hospitalizations and death for those at risk," Zients said.

The pill is easier to deliver than previous treatments, which had to be given by injection or infusion, but requires a prescription and swallowing dozens of pills over 5 days. The drug works best when given within 5 days of symptom onset and not well at all after 7 days, studies show. Some hospitals and pharmacies are working to reduce the time between a positive test, receipt of a prescription and access to the pills.

The antiviral became more important in recent days as the omicron variant took over from delta. The two most used monoclonal antibodies, which also help prevent people from becoming severely ill, are not expected to be effective against omicron, though a third, sotrovimab from GlaxoSmithKline and Vir Biotechnology, continues to be useful.