COVID-19 live updates: City sees fourfold increase in pediatric hospitalizations

Dr, Anthony Fauci on Tuesday called omicron's spread "unprecedented."

"It is really extremely unusual," he told "Good Morning America." "It's a doubling time of two to three days, closer to two days. Which means that if you start off with a few percentage of the isolates being omicron, and you do the math and double that every couple of days, it's not surprising that just a week or two ago we had only 8% to 10%, and now we have 73% of all the isolates are omicron. That's truly unprecedented in the rapidity with which a virus spreads."

Fauci predicted omicron's peak will be soon.

"It's going to be a matter of a couple of weeks that we then start to see just as dramatic a decline," he said. "That's what we're hoping for."

"When you have something that goes up this quickly, often you see it come right back down. Because what will happen is that either almost everyone is either going to get infected, particularly the unvaccinated, or be vaccinated," he said. "And the vaccinated people will either be -- particularly the boosted people, and it's very important to underscore right now the importance of getting boosted -- that those people will either be protected from infection, or if they do get infected, they'll have a relatively mild course of infection."

World Health Organization Director-General Dr. Tedros Adhanom Ghebreyesus on Monday recommended delaying or canceling holiday events, saying, "an event canceled is better than a life canceled."

Fauci told "GMA" that family gatherings are safe if you know everyone is vaccinated.

"When you have a family setting, for example, parents, grandparents, children, who are vaccinated, you should have an enjoyable Christmas and holiday gathering, dinner, whatever in your own home," Fauci said. "What you want to stay away from is indoor congregant sittings in which you do not know the vaccination status of the people around you. That would be quite risky."

The Broadway shows "Harry Potter and the Cursed Child" and "Hadestown" canceled their Christmas week performances, citing rising breakthrough COVID-19 cases.

"We will enchant you another time and apologize for the inconvenience," said a notice posted on the "Harry Potter" Twitter account late on Monday night.  

The two shows added to a growing list of those cancelling performances amid the spread of the omicron variant. "Hamilton" and "Aladdin" both announced they'd stay dark until after Christmas.

Another Broadway musical, "Jagged Little Pill," based on Alanis Morissette's catalog, said on Monday it would close its doors for good.

The producers of "Pill" said in a Twitter post that the spread of the omicron variant "appears to be another substantial public health crisis." Members of the production's company tested positive for COVID-19, the post said.

President Joe Biden was exposed to a staff member who recently tested positive for COVID-19, White House press secretary Jen Psaki said in a statement Monday evening.

Biden was near the staff member for about 30 minutes on Air Force One on Friday, during a trip to Philadelphia from South Carolina, according to Psaki.

The staff member, who is fully vaccinated and boosted, tested negative Friday morning, but tested positive Monday, according to the White House.

The president received an antigen test Sunday and a PCR test Monday, and both came back negative, Psaki said in a statement. He will receive another test Wednesday, she said.

"As CDC guidance does not require fully vaccinated people to quarantine after an exposure, the president will continue with his daily schedule," Psaki said in a statement.

-ABC News' Sarah Kolinovsky

Health officials in Texas announced Monday that it recorded the first death related to the omicron COVID-19 variant.

This is believed to be the first known recorded omicron death in the U.S.

Harris County Health officials would only say the victim was "a man in his 50s," who was unvaccinated and had underlying health conditions..

Public health officials do not think omicron is more virulent than previous variants, but they do say in general vaccination and a booster shot when eligible appears to lower your risk for severe illness.