Anthony Fauci, director of the National Institute of Allergy and...

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, before receiving his first dose of the vaccine on Tuesday. Credit: Getty Images/Pool

The United States is headed for a "post-seasonal" surge of the coronavirus pandemic, following mass global travel and congregating in homes for the holiday season, with the worst still likely to occur, Dr. Anthony Fauci, the nation's top infectious disease specialist, said Sunday.

"We very well might see a post-seasonal, in the sense of Christmas, New Year's, surge, and, as I have described it, as a surge upon a surge," Fauci said on CNN's "State of the Union."

Pointing to spiking hospitalizations and daily deaths, Fauci told CNN anchor Dana Bash: "We're really at a very critical point. If you put more pressure on the system by what might be a post-seasonal surge because of the traveling and the likely congregating of people for the good, warm purposes of being together for the holidays, it's very tough for people to not do that."

Fauci said he agreed with recent remarks from President-elect Joe Biden, made Tuesday, that the worst is not behind us. "I share the concern of President-elect Biden that, as we get into the next few weeks, it might actually get worse," Fauci said.

On Tuesday, Biden said during a news conference, "One thing I promise you about my leadership during this crisis: I'm going to tell it to you straight. I'm going to tell you the truth. And here's the simple truth: Our darkest days in the battle against COVID are ahead of us, not behind us."

U.S. Surgeon General Jerome Adams addressed the possibility of a post-holiday surge in an interview on ABC's "This Week."

"We always see a little bit of a bump after holidays and sometimes a large bump," Adams said.

Also Sunday, Fauci said 70% to 85% of the public would likely need to be vaccinated to achieve "herd immunity," a phenomenon where enough members of the public become immune because they have been infected or were made resistant through the vaccine, rendering the virus largely ineffective.

"I think 70 to 85 percent for herd immunity for COVID-19 is a reasonable estimate. And, in fact, most of my epidemiology colleagues agree with me," he said.

He noted that if the general public began getting vaccinated by April, it would take several months to finish vaccinating them to a level of 70% to 85% by summer's end. "I hope, I hope, that by the time we get to the fall, we will reach that critical percentage of people that we can really start thinking about a return to some sort of normality," Fauci said.

Adm. Brett Giroir, assistant secretary for Health and Human Services, said on "Fox News Sunday," that "nobody knows exactly the number, but based on mathematical models as we have it right now, it is somewhere between 70 and 80 percent of individuals having gotten the vaccine or having gotten the natural infection."

He continued, "somewhere in that 70 to 80 percent range is probably the sweet spot."

Giroir said the U.S. is on track to have distributed 20 million vaccines by the first week in January. Any American who wants a vaccine should be able to receive a dose by June, he said.

"We expect another 30 million in January, another 50 million in February. And with the current contracts, even with just the vaccines we have right now, we still expect that any American who wants a vaccine can be vaccinated by June. That's really very exciting. That means a couple hundred million people being able to be vaccinated by that time."

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