"When you have the kind of inflection that we have, it doesn't all of a sudden turn around like that," said Fauci, the director of the National Institute of Allergy and Infectious Diseases, on ABC's "This Week."
"Clearly in the next few weeks, we're gonna have the same sort of thing," he told "This Week" co-anchor Martha Raddatz, noting that the U.S. "may see a surge upon a surge" of additional new cases due to Thanksgiving gatherings and travel. "We don't want to frighten people, but that's just the reality."
"We said that these things would happen, as we got into the cold weather and as we began traveling, and they've happened. It's going to happen again." Fauci said on "This Week." "So I cannot see, all of a sudden, a relaxation of the kinds of recommendations or restrictions because we're getting into colder weather, and in -- in an even larger holiday season as people travel to come back and forth for Christmas."
Given the increasing number of cases, Fauci urged Americans Sunday to be "really careful" as they return from Thanksgiving holiday travel, encouraging quarantines and testing.
"If they've been in situations outside of the family setting, in which they really don't know the level of exposure … you've really got to understand the importance of trying to prevent further spread and further surge," he said.
On Friday, the U.S. surpassed 13 million total COVID-19 cases, an increase of more than one million cases in six days, according to data from John Hopkins University. Despite the dire data however, Fauci encouraged optimism about the end of the pandemic when asked by Raddatz about continued restrictions.
"Vaccines are really right on the horizon. We'll be having vaccines available for the higher-priority people towards the middle and end of December and as we get into January and February," he said, echoing forecasts from the government's immunization initiative leaders, while still encouraging social distancing, mask wearing and hand washing, among other interim steps to combat the virus.
The public's willingness to receive that vaccine has been a focus of public health experts in recent weeks, even as pharmaceutical companies like Moderna and Pfizer announce promising test results. Recent polls show as many as two out of five Americans would not agree to be vaccinated against COVID-19.
On "This Week," Fauci noted that while the government cannot mandate a vaccine, "any individual group," such as businesses and schools could require its receipt, using his employer, the NIH, and its vaccine requirements for employees as an example. He further encouraged the government to engage with local leaders to assist in combating anti-vaccine rhetoric and affirm the inoculation's safety.
"We've got to be able to get out there, get community people -- who the community trusts -- to show two things: The process of the development of this vaccine has been one that has been scientifically sound, safety has not been compromised, scientific integrity has not been compromised. And the process of determining whether it works, whether it's safe and effective has been independent, by independent bodies and transparent," Fauci said.
Raddatz also asked the doctor for his reaction to the Supreme Court's decision last week to strike down New York's pandemic-induced restriction on large religious gatherings -- a controversial ruling at the intersection between personal and religious freedoms and public safety.
"(Legal challenges) happen… there's nothing I can do about it," Fauci said. "I can just say, it doesn't matter who you are, where you are -- when you have congregate settings, particularly indoors, when people are not wearing masks, that is a considerable risk for acquisition and spread of infection. No matter what the circumstance is, that is a risk."
New York was also the setting of a public school shut-down earlier this month as the virus again spread through New York City and its school district, the nation's largest. On Sunday morning the city announced it would reopen its elementary schools amid criticism that the threshold to close them was lower than other public places. With a variety of strategies being employed across the country to keep schools open, Raddatz asked Fauci how he might advise the incoming administration of President-elect Joe Biden how to formulate a more "unified response."
"We get asked it all the time. You know, we say it -- not being facetiously, as a sound bite or anything -- but, you know, close the bars and keep the schools open is what we really say," he said. "Obviously, you don't have one size fits all. But as I said in the past … the default position should be to try as best as possible within reason to keep the children in school or to get them back to school."
"If you mitigate the things that you know are causing spread in a very, very profound way -- in a robust way -- if you bring that down, you will then indirectly and ultimately protect the children in the school because the community level is determined by how things go across the board," Fauci added.
This report was featured in the Monday, Nov. 30, 2020, episode of “Start Here,” ABC News’ daily news podcast.
"Start Here" offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, Spotify, the ABC News app or wherever you get your podcasts.