President-elect Joe Biden is planning a vaccination program that would inoculate 50 million Americans against COVID-19 in his first 100 days in office.

"This team will help get at least 100 million COVID-19 vaccine shots into the arms of Americans in 100 days," the president-elect said in a speech on Tuesday. A transition team official clarified afterward that 50 million Americans would be vaccinated — because the two most promising early vaccines require two shots per person.

Those vaccinations will be "one of the hardest and most costly operational challenges in our nation's history,” Biden said. Operation Warp Speed, the Trump administration program to fast-track the development of coronavirus vaccines, is currently aiming to vaccinate 100 million people by the end of February.

While laying out his plan, he acknowledged that in order for it to work, it will require the cooperation of lawmakers in Congress to fund the program. If Republicans win two runoff elections in Georgia and retain control of the Senate, that is likely to be a challenge.

Biden also reiterated that he will mandate wearing masks for his first 100 days in office in every area he has the authority to do so — on federal grounds, and during interstate travel. Acknowledging the limits of that authority, he said he would “speak directly to the American people” and ask them to "Wear a mask for the first 100 days … whatever your politics or your point of view."

He added that he believes the majority of schools nationally could be reopened by the end of his first 100 days.

"It should be a national priority to get our kids back into school and keep them in school," he said.

The president would not have the authority to directly reopen schools, but could use federal funding and other incentives to influence those decisions on a state and local level.

Biden announced the vaccination goal on Tuesday as he officially introduced key nominees and appointees on his healthcare team, including California Attorney General Xavier Becerra for secretary of the Department of Health and Human Services, Vivek Murthy for surgeon general — a role Murthy also filled during the Obama administration — Rochelle Walensky to direct the CDC, Marcella Nunez-Smith to chair the COVID-19 equity task force, and Anthony Fauci to be chief medical adviser to Biden on the pandemic.

“These actions are bold, but they are doable and essential to help the public avoid unnecessary risks, to help us save lives, reopen schools and businesses, and to eventually beat the pandemic,” Fauci said in a prerecorded video statement at the Biden event. “I look forward to advising you on these most urgent priorities, and to work with this team of World Class experts who I have known for many years, and deeply respect.”

Fauci was not present or mentioned at a vaccine event held at the same time by President Donald Trump at the White House, except for in a clip in a video that aired at the start of the event that criticized experts, Biden, and others for doubting Trump’s vaccine timeline.

Trump at the event signed an executive order that he said would ensure Americans have priority access to the vaccines when they begin to be distributed globally. It wasn’t clear whether the order would change anything about how the vaccines will actually be distributed — the head of Trump’s vaccine program, Moncef Slaoui, said, “Frankly, I don’t know, and frankly, I’m staying out of this. I can’t comment. I literally don’t know,” when asked how Trump’s executive order on vaccines would make a difference during an interview with Good Morning America on Tuesday morning.

The executive order was signed just one day after the New York Times reported that Trump turned down a deal this summer to secure more vaccine doses from Pfizer. The company signed a deal to provide 100 million doses of the vaccine to the US and is expected to become the first vaccine to receive emergency authorization from the FDA later this week. Pfizer has since signed other deals with foreign governments. The UK began vaccinating its population with Pfizer’s vaccine on Tuesday.

During a phone briefing with reporters on Monday, a senior administration official was unable to provide any further details on how the executive order would work to ensure Americans were prioritized for more vaccines. He said that they expect 40 million doses to be available for the first 20 million people this month and that enough doses would be available to vaccinate all Americans by the end of the second quarter of 2021.

“We think by spring we’re going to be in a position that nobody would have believed possible,” Trump said. “They say it’s somewhat of a miracle.”

Representatives from Pfizer and Moderna were not present at the summit Tuesday. Stat News reported that the drug manufacturing companies declined invitations to attend.

Trump, who during the event again refused to accept that he had lost the election, generally displayed a radically different approach to the vaccine on Tuesday from Biden. The president-elect’s decision to appoint Nunez-Smith to lead a pandemic task force focused on equity is one of several significant departures from how Trump has evaded and downplayed the crisis — Trump has never acknowledged that people of color have been disproportionately hit by the virus itself and its economic fallout. But the Biden team has yet to detail how that task force would reduce inequities in COVID-19 treatment and vaccination.