The Biden administration is set to pay Pfizer Inc $5.29 billion for ten million courses of its COVID-19 pill.

This deal is the U.S.'s largest purchase agreement for a Covid therapy so far - about twice the size of the government's contract with Merck for its Covid drug, which is currently under review at the Food and Drug Administration (FDA).  

In clinical trial data released earlier this month, Pfizer said its  pill reduced hospitalizations and deaths by 89 percent among high-risk adults who had early-stage Covid symptoms.

If Pfizer's drug is authorized by the FDA, it could play a large role in reducing Covid's severity as the virus continues to spread across America and around the world this winter.

On Tuesday, Pfizer asked the FDA to authorize emergency use of its antiviral Covid pill.

The drug works by blocking a key piece of the coronavirus' structure, preventing the virus from multiplying in the body.

Patients take it in a five-day regimen, including three pills in the morning and three pills at night, in combination with a second antiviral pill that boosts the Pfizer drug's impact.

In Pfizer's clinical trial of the drug, this pill decreased patients' risk of Covid hospitalization or death by 89 percent when they started the drug regimen within three days of their symptoms beginning.