EXCLUSIVE: President Biden on Tuesday is expected to direct health officials to double the U.S. government's purchase of Pfizer's antiviral COVID-19 pill from 10 million to 20 million treatment courses and will accelerate the delivery of those treatments, a senior administration official told Fox News.

The Food and Drug Administration granted emergency use authorization for Pfizer's Paxlovid-nirmatrelvir tablets and ritonavir tablets last month – the first oral antiviral treatment for COVID-19.

The Biden administration, in November, announced its commitment to secure 10 million treatment courses of Pfizer's Paxlovid oral antiviral drug, contingent on the FDA's EUA. The administration paid $5.295 billion for the first 10 million courses. 

This image provided by Pfizer in October 2021 shows the company's COVID-19 Paxlovid pills. U.S. health regulators on Wednesday, Dec. 22, 2021 authorized the first pill against COVID-19, a Pfizer drug that Americans will be able to take at home to head off the worst effects of the virus. (Pfizer via AP) (Pfizer via AP)

The drug has been developed to treat non-hospitalized, symptomatic adults diagnosed with COVID-19 who are at increased risk of progressing to severe illness that could lead to hospitalization or death.

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A senior administration official told Fox News that Pfizer's pills "fit into the diverse portfolio of treatments we have for folks that get COVID." 

"When it comes to COVID-19 therapeutics, we have approached it like filling a medicine cabinet – we are not relying on one type, or one brand, or one treatment," the official told Fox News. "We ensured that we would invest in and buy a broad variety – across monoclonal antibodies, pre-exposure prevention treatments, and antiviral pills." 

The official told Fox News that in the month of January, the administration will have more therapeutics that work against circulating variants, both delta and omicron, "than ever before in the pandemic," saying there will be close to 4 million treatment doses available. 

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Biden is scheduled to meet with his COVID-19 response team Tuesday afternoon to receive an update on the omicron variant, and to discuss his administration's response. 

Health officials are set to brief the president on the latest resources and personnel being sent to states and local communities to help with staffing needs and hospital capacity, as well as the ongoing work to expand access to COVID-19 treatments. 

As for the omicron variant, health officials are expected to say that while cases continue to increase, fully vaccinated and boosted Americans that get infected are not likely to have severe symptoms. 

Following his briefing, the president is expected to announce the updates, including the government's purchase of the 10 million additional doses of the Pfizer pill, in brief remarks Tuesday afternoon. 

Biden is set to highlight Pfizer's Paxlovid, and will cite studies that show the treatment can "greatly reduce the chances of hospitalization and death for those at high risk of severe outcomes from COVID." 

Paxlovid is a protease inhibitor designed to block an enzyme the SARS-CoV-2 virus needs to replicate in human cells. Protease inhibitors are a class of drugs that prevent viruses from replicating within cells in the human body, which renders them unable to multiply and spread within the body, according to the Department of Health and Human Services. 

The pill can treat mild-to-moderate coronavirus disease in adults and children 12 years of age or older weighing at least 40 kilograms or about 88 pounds. An individual can only use the drug is they meet those qualifications, have tested positive for COVID-19, and who "are at high risk for progression to severe COVID-19, including hospitalization or death," the FDA said last month.

Paxlovid is available by prescription only and should be initiated as soon as possible after diagnosis of COVID-19 and within five days of symptom onset. 

Paxlovid is not authorized for the pre-exposure or post-exposure prevention of COVID-19 or for initiation of treatment in those requiring hospitalization due to severe or critical COVID-19. Paxlovid is not a substitute for vaccination in individuals for whom COVID-19 vaccination and a booster dose are recommended, the FDA said.

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The FDA still "urges the public to get vaccinated and receive a booster if eligible."

Paxlovid consists of nirmatrelvir, which inhibits a SARS-CoV-2 protein to stop the virus from replicating, and ritonavir, which slows down nirmatrelvir’s breakdown to help it remain in the body for a longer period at higher concentrations, the FDA said. 

Treatment involves taking three tablets – two tablets of nirmatrelvir and one tablet of ritonavir – together orally twice daily for five days, for a total of 30 tablets. Paxlovid is not authorized for use for longer than five consecutive days.