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

President Joe Biden will speak to the public at 2:30 p.m. ET Tuesday, announcing new steps to combat the pandemic.

Biden will announce a plan to distribute 500 million free at-home rapid tests to Americans beginning in January. The free at-home rapid tests will be delivered by mail to Americans who request them. Americans will have to request the tests through a website that will launch in January, a senior administration official said.

The president is also set to introduce new federal testing sites around the U.S., the first several of which will launch in New York City by Christmas.

The government will also mobilize 1,000 military doctors and nurses to overburdened hospitals, the senior administration official said. There are currently 175 troops spread over four states, and since August 2021, when a joint military operation across the Army, Navy and Air Force began, about 530 medical military personnel have been deployed to work alongside civilian health care providers.

-ABC News' Cheyenne Haslett, Sarah Kolinovsky

Massachusetts will activate up to 500 National Guard members as the state faces a "critical staffing shortage," Gov. Charlie Baker's office said Tuesday.

Besides a staffing shortage, hospitals are also seeing an influx of patients, but many patients are from "non-COVID related reasons," the office said.

Beginning Dec. 27, all hospitals will be directed to postpone or cancel nonessential elective procedures that are likely to result in hospital admission.

Massachusetts has also updated its mask guidance, recommending that everyone, including those vaccinated, wear a mask in indoor, public places.

-ABC News' Arielle Mitropoulos

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.