(CNN) The United States is likely in for a hard winter as the Omicron variant of Covid-19 spreads rapidly, Dr. Anthony Fauci says, straining a health care system already battered by the Delta variant.
"It's going to take over," Fauci, the nation's top infectious disease expert, said of the Omicron variant on CNN's "State of the Union" on Sunday, urging Americans to get vaccinated and get their booster shots. "And be prudent in everything else you do: When you travel in your indoor settings that are congregated, wear a mask."
"We can't walk away from that, Jake, we can't," he told CNN's Jake Tapper. "Because with Omicron, that we're dealing with, it is going to be a tough few weeks to months as we get deeper into the winter."
According to the World Health Organization, Omicron cases are doubling every 1.5 to 3 days with documented spread. And in the US, it's expected to become the "dominant strain" in the coming weeks, the director of the US Centers for Disease Control and Prevention said Friday.
The US is now facing a resurgent coronavirus as the pandemic marches into its third year: The country was averaging 126,967 new cases per day as of Saturday, according to data from Johns Hopkins University -- up from an average of just over 70,000 new cases per day at the beginning of November.
"This Omicron variant is extraordinarily contagious. It's as contagious as measles, and that's about the most contagious virus that we've seen," CNN medical analyst Jonathan Reiner said Saturday, warning there was a "tsunami" coming for unvaccinated Americans.
Scientists say it's still too early to tell whether Omicron causes a milder form of Covid-19. But regardless, it will put pressure on the health care system, Reiner said.
"Why would you go into that kind of battle completely unarmed?" said Reiner, a professor of medicine and surgery at George Washington University School of Medicine & Health Sciences. "Our vaccines will protect you, particularly if you are triple vaxed. People who are unvaxed should start the process now. Go ahead and go to your pharmacy and get vaccinated."
It's important to remain vigilant to help prevent hospitals from getting "swamped," he added. Even if Omicron ends up causing less severe infection than Delta, the sheer number of infections Omicron could generate could overwhelm US hospitals.
More than 69,000 people are hospitalized with Covid-19 across the US and more than 20% of all ICU beds are occupied by Covid-19 patients, according to the US Department of Health and Human Services.
"We need to protect our health care system," Reiner said, "and that's why every American needs to mask up and vax up right now because our health care infrastructure is at stake right now."
President Joe Biden will meet with his Covid-19 response team regarding the latest developments with the Omicron variant, according to the White House.
The meeting comes ahead of remarks Tuesday in which the President will discuss the variant, new steps the administration is taking and will issue another "stark warning of what the winter will look like for Americans who choose to remain unvaccinated," the White House said.
According to CDC data, about 61.4% of the total US population is fully vaccinated, and about 32.1% of fully vaccinated adults have received a booster, which health officials point to as a crucial line of defense against the Omicron variant. And yet many who are eligible for a booster shot have not gotten one.
The protection offered from two-dose mRNA vaccines -- like those produced by Pfizer/BioNTech and Moderna -- is "quite good particularly against severe disease," Fauci said Sunday.
"But when you get to Omicron, the protection significantly goes down," he said. "But the good news is when you boost someone, it goes right back up."
Unvaccinated people face a 20 times greater risk of dying from Covid-19 and a 10 times greater risk of testing positive than fully-vaccinated people who have also received a booster, according to data recently published by the CDC.
The data suggests the gap in risk between unvaccinated people and those with a booster is even larger than it is between unvaccinated people and those who are fully vaccinated with their initial series.
Dr. Francis Collins, the outgoing director of the National Institutes of Health, told CBS' "Face the Nation" on Sunday people should not wait to get boosted.
"A big message for today is, if you've had vaccines and a booster, you're very well-protected against Omicron causing you severe disease," he said. "So anybody listening to this who is in that 60% of Americans who are eligible for a booster but haven't yet gotten one, this is the week to do it. Do not wait."
On Sunday, New York state broke its record for the highest single-day Covid-19 case count since the beginning of the pandemic for a third consecutive day. Gov. Kathy Hochul's office reported 22,478 positive cases Sunday, up from 21,908 positive Covid-19 cases Saturday.
Hochul reiterated her message to New Yorkers that despite surging numbers, they are in a far more favorable position than when the virus initially struck the Empire State last year.
"This is not March of 2020, we are not defenseless," she said in a statement Sunday. "We have the tools to protect ourselves and the vulnerable (loved) ones in our families: Get vaccinated, get the booster and wear a mask when indoors or in large gatherings. Don't take a chance during the winter surge."
Covid-19 hospitalizations across the state remained relatively low at 3,909, compared to a peak of 18,825 Covid-19 related hospitalizations on April 13, 2020, according to available data.
"This is not like the beginning of the pandemic," Hochul said in a statement Saturday. "We are prepared for the winter surge because we have the tools at our disposal."
New York Mayor Bill de Blasio echoed that message in a news conference Sunday, pointing, in part, to the availability of vaccines and boosters.
"We're not here to minimize the extent of the challenge -- it will be very challenging," the mayor said. "But it is something that we can meet. It is something we can overcome. We have the tools, but we need everyone to get in the game."
In New York City, Covid-19 cases more than doubled from the beginning of the week on December 13 to Saturday. On Sunday de Blasio reported a seven-day average of 5,731 new cases, a number he called "a really, really shocking figure and one that will keep growing, undoubtedly."
In response, the city is also working to increase access to Covid-19 testing, the mayor said.
"You'll be seeing new testing sites, you'll be seeing more at-home testing kids being made available through community organizations," he said. "All of these efforts will help to reduce the lines we're seeing at testing sites and help to make testing more available."
At one testing site in Brooklyn, resident Rich Odior told CNN he waited two hours Sunday to get a test. He's vaccinated but has friends who've gotten Covid-19 or had scares, so he wanted to try to "play it safe for the family."
Kymoi Phillip said he similarly felt getting a test was a safe choice because "you never know who could have (a) case."
Being a student, Phillip said, he was concerned hearing of all the schools that have decided to close. "I'm afraid that my school might be getting shut down and we might go back into lockdown," adding he fears "we may be in the same predicament that were were in last year."
The surge has already affected the city's entertainment industry, fording the cancellation of a number of Broadway shows in recent days -- just months after Broadway began welcoming audiences back after an extended pandemic hiatus.
This weekend's "Saturday Night Live" had no in-studio audience and aired mostly pre-taped segments because of the rise in Covid-19 cases.
The move followed the cancellation of the Radio City Rockettes' "Christmas Spectacular" shows for the rest of the year.
New York isn't the only state grappling with a surge in cases or anxiety about what's to come.
Maryland is bracing for what Gov. Larry Hogan, a Republican, on Sunday said could be the "worst surge we've seen in our hospitals throughout the entire crisis," telling "Fox News Sunday" hospitalizations are already up about 150% over the past two weeks.
California health officials said Friday they were seeing hospitalization numbers begin to trend upward, stressing the need for vaccinations and booster vaccines.
In New Jersey, "we're seeing long lines outside of our testing clinic, more demand than we've seen in many months for testing, because folks are getting sick," said Dr. Shereef Elnahal, president and CEO of University Hospital in Newark.
Hospitalizations have doubled over the past two weeks, he said, and although 46% of those hospitalized earlier this week had been vaccinated, they had not had a booster shot.
Dr. Rob Davidson, an emergency room physician in Michigan, said he's seeing a "pretty critical Delta surge right now." And while he's seeing the test positivity rate slightly decrease, Covid-19 patients are staying in the hospital for extended periods of time.
Dr. Marc Gorelick, who heads Children's Minnesota hospital, said the facility is already struggling to cope with the numbers.
"When you're on top of a surge where you're already at 90%, 95% capacity, those extra ... preventable Covid patients coming in are the thing that pushes the system to the brink," Gorelick said Friday.
Oregon officials forecast a grim early 2022: Dr. Peter Graven, a data scientist for Oregon Health and Science University, said a surge in the state's hospitalizations could be expected by mid-January.
"Combined with its heightened transmissibility, we expect Omicron will generate a large increase in the number of Oregonians that will become severely ill and likely need a hospital."
Scientists are still working to gather information on how severe the Omicron variant is.
Data from two weeks of South African cases appeared to indicate Omicron was milder in severity. But UK epidemiologists said last week they found no evidence Omicron is causing milder disease there -- although the Imperial College London team also said there was not much data to go on yet.
The CDC looked at 43 cases of Omicron and most of those people had mild symptoms, it said last week. Most were vaccinated, with about a third of the total group boosted.
"We've seen cases of Omicron among those who are both vaccinated and boosted, and we believe these cases are milder or asymptomatic because of vaccine protection. What we do know is we have the tools to protect ourselves against Covid-19. We have vaccines. We have boosters," CDC Director Dr. Rochelle Walensky said Friday.