Dr. Anthony Fauci and White House coronavirus response coordinator Dr. Deborah Birx warned Tuesday that the U.S. hasn't yet seen the full impact of Thanksgiving gatherings.

“We have not yet seen the full blunt and the effect of the traveling and the congregating,” Fauci said at The Wall Street Journal's CEO Council summit .“That should be sometime probably next week, or a week and a half.”

"Then we're going to enter into the Christmas season, again, with more traveling and with more congregating at family and social gatherings. So we're in for a very challenging period," Fauci continued. "And the only way we're going to counter that is by a consistent uniform implementation and adherence to public health measures."

Fauci also said he’s accepted President-elect Joe Biden’s offer to become his chief medical adviser.

“I've already told the president-elect that I would gladly accept that responsibility. It really is very similar to what I'm doing now,” Fauci said.

ABC News' Anne Flaherty contributed to this report.

The University of Michigan said this Saturday's football game against Ohio State is now canceled due to "an increasing number of positive COVID-19 cases and student-athletes in quarantine over the past week."

"The number of positive tests has continued to trend in an upward direction over the last seven days," said Michigan's Athletic Director, Warde Manuel. "We have not been cleared to participate in practice at this time. Unfortunately, we will not be able to field a team due to COVID-19 positives and the associated quarantining required of close-contact individuals."

ABC News' Josh Hoyos contributed to this report.

Nearly 1.5 million children in the U.S. have tested positive for COVID-19 since the pandemic began, the American Academy of Pediatrics and the Children’s Hospital Association said in its weekly report.

During the week ending Dec. 3, there were 123,688 new cases of children with COVID-19, bringing the total number of U.S. children diagnosed to 1,460,905.

ABC News' Eric Strauss contributed to this report.

Scientists from the U.S. Food and Drug Administration on Tuesday appeared set to confirm that the Pfizer/BioNTech COVID-19 vaccine is safe and effective against the virus, according to documents released ahead of a crucial meeting on the vaccine this week.

According to a document prepared by FDA staff, government scientists plan to tell the advisory committee that the data is adequate to determine the vaccine is both safe and effective.

While that doesn't mean the FDA is prepared to authorize it just yet, the briefing materials suggest agency staff aren't warning of any last-minute issues.

"Safety data from approximately 38,000 participants [greater than or equal to] 16 years of age randomized 1:1 to vaccine or placebo with a median of 2 months of follow up after the second dose suggest a favorable safety profile, with no specific safety concerns identified that would preclude issuance of an EUA," the FDA wrote.

The report notes the most common reaction was a skin reaction at the injection site, followed by fatigue or headaches.

The FDA released data on the Pfizer/BioNTech vaccine trials and the agency's scientific analysis ahead of an advisory committee meeting on Thursday, when independent experts are set to discuss and vote on whether to recommend the vaccine be authorized for emergency use.

ABC News' Stephanie Ebbs and Anne Flaherty contributed to this report.

U.S. Surgeon General Jerome Adams urged people to take the coronavirus pandemic seriously and follow public health guidelines as infections and hospitalizations soar across the country.

"I want the American people to know this virus is incredibly unforgiving, cases are going up, hospitalizations are going up, my colleagues are dog-tired and we need you to hang on just a little bit longer because we've got vaccines coming but we want as many people to be alive to get them as possible and a lot of that is going to depend on your behavior," Adams told ABC News chief anchor George Stephanopoulos in an interview Monday on "Good Morning America."

Although "more people than ever are wearing masks," Adams said he's "very" concerned by the number of people who still "don't understand how much spread is occurring by people who don't have symptoms."

About 20 million "full doses" of COVID-19 vaccines will be available by the end of the year, according to Adams, who urged every American to be immunized against the virus as soon as a vaccine is authorized and made available.

"It's a way that we can ultimately end this pandemic, but it doesn't matter if people won't get the vaccination," the surgeon general said. "We know that vaccine levels are only about 50% for adults for flu and they go down to about 40% for African-Americans."

Adams said he is working with historically black colleges and universities as well as faith communities to bolster vaccine confidence among all populations. The White House is also hosting a vaccine summit Tuesday, he said.

"One thing you can all do right now, it's national flu immunization week, get your flu shot because half a million people were hospitalized last year with the flu," Adams said. "We simply can't afford for that to happen this year with hospitals being overwhelmed."

The surgeon general said the current surge in infections across the country "is different than earlier surges," because it's not about a lack of masks or personal protective equipment, nor is it due to a lack of testing.

"It's really about health care capacity, and certain places are just being overwhelmed," he said. "So we know that we can actually help them with their health care capacity by immunizing their health care staff. We're going to leave it up to the states, but we're going to give them guidance."

Adams noted it's also important to vaccinate those who are most likely to die from COVID-19.

"We know that 40 to 50% of the deaths are occurring in people who are in longterm care facilities who are older," he said.