(Bloomberg) -- President-elect Joe Biden vowed Tuesday to get 100 million doses of a coronavirus vaccine distributed to Americans in the first 100 days of his administration.

Biden said getting vaccines to most Americans would be a costly challenge and called on Congress to designate funds for getting vaccine to the people who need it.

“This will be one of the hardest and most costly operational challenges in our nation’s history,” he said at an event to introduce his health team.

“We need Congress to finish the bipartisan work that’s underway now or millions of Americans might wait months longer to get the vaccine,” he said. “Developing a vaccine is only one herculean task. Distributing it is another herculean task.”

He also called on all Americans to wear masks in public for those 100 days to slow the spread of the virus until vaccination is more widespread and vowed to prioritize the reopening of schools.

“Whatever your politics and your point of view, mask up for 100 days when we take office. One hundred days to make a difference,” he said. “It’s not a political statement, it’s a patriotic act.”

Biden spoke as President Donald Trump was holding a vaccine summit at the White House amid news that available doses of one vaccine will be far less than expected.

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