The Biden administration expects to take delivery of 265,000 courses of Pfizer Inc.’s newly authorized COVID-19 treatment pill in January.

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.

Eventually, Americans will be able to take at home to head off the worst effects of the virus. It will be provided free of charge. (Merck’s pill also gained federal approval this week but Pfizer’s pill is expected to be the treatment option of choice due to superior results in testing.)

Meantime, health officials agree vaccinations and boosters are the best way to combat the coronavirus and try to slow transmission of the surging omicron variant.

The U.S. will pay about $500 for each course of Pfizer’s treatment, which consists of three pills taken twice a day for five days. Two of the pills are Paxlovid and the third is a different antiviral that helps boost levels of the main drug in the body. The new drug, 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.

Here is who is eligible to take the pill under the Food and Drug Administration authorization:

–Adults and children ages 12 and older with a positive COVID-19 test and early symptoms who face the highest risks of hospitalization. Patients will need a positive COVID-19 test to get a prescription.

–Children eligible for the drug must weigh at least 88 pounds (40 kilograms).

–Highest risk includes older people and those with conditions like obesity and heart disease. However, the drug is not recommended for patients with severe kidney or liver problems.

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.

Pfizer’s drug is part of a decades-old family of antiviral drugs known as protease inhibitors, which revolutionized the treatment of HIV and hepatitis C. The drugs block a key enzyme which viruses need to multiply in the human body.

It was not tested on omicron but officials believe it will be effective against the surging variant.

The production of Pfizer’s pill is expected to steadily escalate, with the U.S. receiving its full order of 10 million courses by July, the officials said.