Scott Gottlieb, former FDA commissioner and current Pfizer board member, confirmed on Tuesday that the Trump administration turned Pfizer's offer for an additional 100 million coronavirus vaccine doses last summer, as the New York Times first reported.

Why it matters: With Pfizer and Moderna the only two manufacturers that have applied for emergency approval from the FDA thus far, vaccine supplies in the U.S. are expected to be too scarce to rapidly inoculate the entire population.

• After signed its advance contract with the U.S. government for an initial 100 million doses, Pfizer went on to negotiate an agreement to supply the European Union with 200 million doses.
• Pfizer is now negotiating with the Trump administration to provide more vaccine doses, but the company cannot guarantee that it will deliver more than the initial 100 million before the summer, per the NYT.

What he's saying: "Pfizer did offer an additional allotment coming out of that plan, basically the second quarter allotment, to the U.S. government multiple times — and as recently as after the interim data came out and we knew this vaccine looked to be effective,"Gottlieb said in an interview with CNBC.

• "I think the government made a bet that they are going to option or advance purchase vaccine from multiple manufacturers. They have agreements now with five or six manufacturers for about 100 million doses each manufacturer. They want to spread those bets," he continued.
• "I think they're betting that more than one vaccine is going to get authorized and there will be more vaccines on the market, and that perhaps could be why they didn't take up that additional 100 million option agreement."

The other side: "We are confident that we will have 100 million doses of Pfizer’s vaccine as agreed to in our contract, and beyond that, we have five other vaccine candidates, including 100 million doses on the way from Moderna," a Department of Health and Human Services spokesperson told the NYT.

• President Trump is expected to sign an executive order on Tuesday that aims to prioritize the shipment of the vaccine to the U.S. over other countries, according to CNN.
• Asked to explain how this order would work, however, Operation Warp Speed chief scientist Moncef Slaoui told ABC's "Good Morning America": "Frankly, I don't know."

The big picture: Pfizer and Moderna are the only two vaccine manufacturers up for emergency approval in the U.S., other makers like AstraZeneca, Johnson & Johnson and Novavax have yet to present results for their respective vaccines.

• The U.S. has a population of around 330 million people, but the initial Pfizer doses would only be enough to inoculate 50 million people since the vaccine requires two shots.
• The government's top infectious disease expert Anthony Fauci has said that for the country to return to normal, 70-75% of Americans will need to get vaccinated.