(NBC News) - The single, urgent mission to defeat COVID-19 is running on two very separate tracks.

President-elect Joe Biden on Tuesday introduced nominees for his health team and listed priorities to tackle the COVID crisis.

"Masking, vaccinations, opening schools. These are the three key goals for my first 100 days," Mr. Biden said.

At the same time, President Trump hosted a vaccine summit celebrating the expected approval later this week of the first COVID vaccine for U.S. distribution.

"Nobody thought it was remotely possible to do what we've done in the past nine months," Mr. Trump said.

As the president seeks credit, the incoming Biden administration will be responsible for getting the vast majority of Americans vaccinated. Still, no members of his team were and no one was present from drug makers Pfizer or Moderna.

President Trump also signed an executive order aimed at prioritizing COVID vaccines for Americans before other countries, but the chief science advisor behind the government's fast-track process couldn't say what the order would actually do.

It comes amid new reports the Trump administration repeatedly passed on the chance to lock in 100 million extra doses of the Pfizer vaccine, potentially delaying when Americans could access it.

The White House is denying that.

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