Asked how worried Americans should be about omicron and a post-holiday surge, Dr. Anthony Fauci said that if we didn't have vaccines, boosters and masks he'd "really be worried."

"But we have tools. So get vaccinated, get boosted," Fauci said at Wednesday's White House COVID-19 briefing.

CDC Director Rochelle Walensky said the agency expects to see omicron continue to grow.

"What does this mean for individuals and families as we head into the winter months? A time when families may be gathering with one another over the holidays? It means that it is vital for everyone to get vaccinated and boosted if they are eligible," Walensky said.

White House COVID-19 response coordinator Jeff Zients added, "We're not going to shut down our economy in any way. We're going to keep our schools and our businesses open."

-ABC News' Cheyenne Haslett

The United Kingdom confirmed 78,610 COVID-19 cases in the last 24 hours -- the highest daily number since the start of the pandemic, officials said Wednesday.

Prime Minister Boris Johnson encouraged everyone to continue to get vaccinated and boosted. He said 650,000 boosters were administered Tuesday and now 45% of all adults have received a booster.

-ABC News' Joe Simonetti

School leaders at both New York University and Princeton University announced Wednesday that they will take steps to cancel end-of-year events and move winter exams online amid a surge in COVID-19 cases on their respective campuses.

"Given that we've seen an uptick in cases among undergraduates during the last 24 hours -- including suspected cases of the highly contagious Omicron variant -- we hope to avoid letting the final exam schedule interfere with students’ travel home for Winter Break," Princeton University's dean, Jill Dolan, and vice president for campus life, Rochelle Calhoun, said in a joint statement. "We certainly don’t want you remaining on campus in required isolation through the holidays."

All indoor gatherings with food and those where face coverings cannot be worn must be canceled or postponed at Princeton's New Jersey campus from Thursday through Jan. 7, according to the statement.

A statement from New York University's provost, Katherine Fleming, executive Vice President, Martin Dorph, and head of the COVID-19 prevention and response team, Dr. Carlo Ciotoli, said they "strongly encourage that final examinations and/or assessments be changed to remote/online format." All discretionary, non-essential, non-academic gatherings and events at the school's campus in New York City must be canceled "immediately," according to the statement.

"The continuous review of the data from our COVID-19 testing program has indicated a considerable acceleration in the rate of new cases in our community," they said. "It’s not a cause for alarm, but it is a cause for concern, caution, and appropriate actions."

NYU has also joined a growing list of colleges and universities across the nation that are requiring all eligible members of the school community, including faculty and students, to be fully vaccinated against COVID-19 and receive a booster shot ahead of the upcoming spring semester.

Meanwhile, officials at Cornell University in Ithaca, New York, announced Tuesday that they have moved the campus into a "level red" alert after identifying evidence of suspected cases of the omicron variant in a "significant" number of the school's COVID-19 positive samples from students.

According to data from the Centers for Disease Control and Prevention, the omicron variant is estimated to account for more than 13% of newly confirmed COVID-19 cases in the New York and New Jersey area -- the highest proportion of any region of the United States.

-ABC News' Chris Donato and Arielle Mitropoulos

A journalist traveling alongside U.S. Secretary of State Antony Blinken on his visit to Southeast Asia has tested positive for COVID-19 in Malaysia, according to U.S. Department of State spokesperson Ned Price.

Meanwhile, Blinken and his senior staff all tested negative for COVID-19 upon arrival in Kuala Lumpur on Tuesday night. The member of the traveling press pool who tested positive had last tested negative in Indonesia's capital, their previous stop, on Tuesday.

"The individual who tested positive will remain in isolation," Price said in a statement Wednesday, "and we will continue to adhere to and go beyond CDC guidance, including with our rigorous testing protocol, for the remaining traveling party."

Blinken has canceled a scheduled trip to Thailand "out of an abundance of caution" and will return home to the United States, according to Price.

"The Secretary expressed his deep regret to the Foreign Minister that he would not be able to visit Bangkok this week," Price said. "He explained that, in order to mitigate the risk of the spread of COVID-19 and to prioritize the health and safety of the U.S. traveling party and those they would otherwise come into contact with, the Secretary would be returning to Washington, D.C. out of an abundance of caution."

"The Secretary extended an invitation for the Foreign Minister to visit Washington, D.C. at the earliest opportunity and noted that he looked forward to traveling to Thailand as soon as possible," Price added. "They affirmed that they would use the upcoming engagements to further deepen the U.S.-Thai alliance."

The U.S. Embassy in Malaysia confirmed that the infected individual "was not involved and has not participated in any of Secretary Blinken's program in Kuala Lumpur."

"The sole member of the traveling party who tested positive is observing all requirements of the Ministry of Health," the embassy said in a statement Wednesday. "We confirm all other members of the party tested negative for COVID-19 upon arrival in Malaysia."

Blinken was in Indonesia on Tuesday, and the U.S. Embassy in Jakarta confirmed that no members of the traveling party tested positive for COVID-19.

All members of the U.S. delegation are required to be vaccinated against COVID-19 and undergo regular testing on trips.

-ABC News' Conor Finnegan

Dr. Anthony Fauci, the nation's leading expert on infectious diseases, warned Thursday that omicron will become the dominant variant of the novel coronavirus in the United States "very soon."

"It has an extraordinary ability to transmit efficiently and spread," Fauci, the chief medical advisor to U.S. President Joe Biden, told ABC News' George Stephanopoulos in an interview on "Good Morning America."

"It has what we call a doubling time of about three days and if you do the math on that, if you have just a couple of percentage of the isolates being omicron, very soon it's going to be the dominant variant," he explained. "We've seen that in South Africa, we're seeing it in the U.K. and I'm absolutely certain that's what we're going to be seeing here relatively soon."

Fauci, who is also the director of the National Institute of Allergy and Infectious Diseases, urged Americans to "absolutely" get vaccinated against COVID-19, if they haven't already, and to also receive a booster shot when they become eligible.

"At this point, we don't believe you need an omicron-specific boost," he added. "We just need to get the boost with what you got originally for the primary vaccination."