Dr. Deborah Birx said Americans "may have made mistakes over the Thanksgiving time period," and urged everyone who attended holiday gatherings last week to assume they are infected with COVID-19 and to get tested this week. Birx, the coordinator of the White House Coronavirus Task Force, made the statements during an appearance on "Face the Nation."

"We know people may have made mistakes over the Thanksgiving time period," Birx said on Sunday. "If you're young and you gathered, you need to be tested about five to 10 days later. But you need to assume that you're infected and not go near your grandparents and aunts and others without a mask."

Birx noted, "We're really asking families to even mask indoors if they chose to gather during Thanksgiving and others went across the country or even into the next state."

Birx warned that she believes there will be massive spikes of coronavirus following Thanksgiving.

"Going into the Memorial Day weekend we had less than 25,000 a day, we had only 30,000 inpatients in the hospital and we had way less mortality, way under a thousand," Birx said. "We're entering this post-Thanksgiving surge with three, four and 10 times as much disease across the country," Birx said during the interview. "And so that's what worries us the most."

"We are deeply worried about what could happen post-Thanksgiving because the number of cases, 25,000 versus 180,000 a day, that's where- that's why we are deeply concerned," she said.

Birx said despite coronavirus cases and hospitalizations falling in the northern plains states, "we're worried that all of that will be reversed" because of Thanksgiving gatherings.

While some governors implement more stringent restrictions as the COVID-19 cases rise, Birx took aim at the freedom-embracing governors and mayors who have allowed their constituents to decide which activities they are comfortable in doing and not doing during the pandemic.

"To every American, this is the moment to protect yourself and your family," Birx stated. "So if your governor or your mayor isn't doing the policies that we know are critical — masking, physical distancing, avoiding bars, avoiding crowded indoor areas — if those restrictions don't exist in your state, you need to take it upon yourself to be restricted. You need to not go to these places. You need to protect your family now."

Birx revealed that she expects to provide a coronavirus briefing to the incoming Biden administration on Monday.

"The one thing that we will bring to the Biden administration in that discussion is to understand how they want to see the data because data isn't helpful if it's not actionable," she said. "And each group needs to see it the way it moves them to action."

Birx will continue to brief Vice President Mike Pence everyday.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said that if United States experiences the current rate of infection then Americans should not hold Christmas celebrations this year.

"What we expect, unfortunately, as we go for the next couple of weeks into December, is that we might see a surge superimposed on the surge we are already in," Fauci said during a "Meet the Press" interview on Sunday. "I don't want to frighten people, except to say it is not too late to do something about this."

Dr. Fauci cautioned that the upcoming holiday season is "a precarious situation."