The FDA has approved the first pill to treat COVID-19, the federal agency said on December 22.

The drug Paxlovid — manufactured by Pfizer, one of the early COVID vaccine makers — is a faster, cheaper way to treat early COVID-19 infections. All of the previous medications approved to treat COVID require an injection or intravenous administration.

An antiviral pill from Merck also is expected to win authorization from the FDA.

Experts said that Pfizer's drug is all but certain to be the preferred option because of its mild side effects and superior effectiveness, including a nearly 90% reduction in hospitalizations and deaths among patients most likely to get severe disease.

"The efficacy is high, the side effects are low, and it's oral. It checks all the boxes," said Dr. Gregory Poland of the Mayo Clinic. "You're looking at a 90% decreased risk of hospitalization and death in a high-risk group — that's stunning."

The FDA authorized Pfizer's drug for adults and children ages 12 and older with a positive COVID-19 test and early symptoms who face the highest risks of hospitalization.

That category includes older people and those with conditions like obesity and heart disease. Children eligible for the drug must weigh at least 88 pounds (40 kilograms).

Both the Pfizer and Merck pills are expected to be effective against Omicron because they don't target the spike protein where most of the variant's worrisome mutations reside.

The US government said it would purchase enough Paxlovid to treat 10 million people, but Pfizer currently has only 180,000 treatment courses available worldwide, with roughly 60,000 to 70,000 allocated to the US. Federal health officials are expected to ration early shipments to the hardest-hit parts of the country.

Pfizer said the small supply is due to the manufacturing time — currently about nine months. The company says it can halve production time next year.

Pfizer says it's on track to produce 80 million courses globally next year, under contracts with the UK, Australia, and other nations.

Health experts agree that vaccination remains the best way to protect against COVID-19. But with roughly 40 million American adults still unvaccinated, effective drugs will be critical to blunting the current and future waves of infection.

The US is now reporting more than 140,000 new infections daily, and federal officials warn that the Omicron variant could send case counts soaring. With those facts in mind, experts warn that Paxlovid's initial impact could be limited.

Scientists warn that Paxlovid has only proven effective if given within five days of symptoms appearing. With testing supplies stretched, experts worry it may be unrealistic for patients to self-diagnose, get tested, see a physician, and pick up a prescription within that narrow window.

"If you go outside that window of time, I fully expect the effectiveness of this drug is going to fall," said Andrew Pekosz, a Johns Hopkins University virologist.

The FDA based its decision on company results from a 2,250-patient trial that showed the pill cut hospitalizations and deaths by 89% when given to people with mild-to-moderate COVID-19 within three days of symptoms. Less than 1% of patients taking the drug were hospitalized, and none died at the end of the 30-day study period, compared with 6.5% of patients hospitalized in the group getting a dummy pill, which included nine deaths.