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WASHINGTON (NEXSTAR) — The nation’s leading infectious disease expert, Dr. Anthony Fauci, warned Friday life in the U.S. may not be back to normal until late 2021.

In an interview with MSNBC, Fauci said he’s confident a vaccine will be available over the next few months but cautions distributing the shot will take time.

“By the time you mobilize the distribution of the vaccine and get a majority or more of the population vaccinated and protected, that’s likely not going to happen until the end of 2021,” he said in the interview with Andrea Mitchell. “If you’re talking about getting back to a degree of normality prior to COVID, it’s going to be well into 2021, towards the end of 2021.”

Fauci again expressed concern over a spike in cases over the winter months where people may huddle up indoors due to cooler temperatures.

“I am concerned when I see things starting indoors, and that becomes more compelling when you move into fall and winter season,” he added.

Earlier this week, Fauci made headlines for saying President Donald Trump’s prediction of a coronavirus vaccine in October was “not impossible” but unlikely.

Fauci added he was “pretty sure” a vaccine would not be approved for Americans unless it was both safe and effective.

In an interview that first appeared on NewsNationNow.com earlier this week, Stephen Hahn, commissioner of the Food and Drug Administration, said the agency would not cut corners as it evaluates vaccines, but would aim to expedite its work.

The Associated Press contributed to this report.