(CNN) — The impact of the Omicron variant of Covid-19 on a largely unboosted US population entering the holiday season will create a “perfect storm” set to sweep health care across all regions of the US, an expert said Monday.

The variant is now the most dominant strain in the US, accounting for over 73% of new coronavirus cases less than three weeks after the first was reported, according to estimates posted Monday by the US Centers for Disease Control and Prevention.

The first confirmed Omicron-related death in the US was reported Monday. The Texas man in his 50s was unvaccinated, with underlying health conditions and had been previously infected with Covid-19, officials said.

Globally, Omicron cases are doubling every 1.5 to 3 days, the World Health Organization says.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told CNN on Monday that Omicron’s far higher transmission levels — compared to Delta — would lead to a rise in US hospitalizations.

“Even though more people who get it have milder illness, so many more people, overall, will get it that I think we are going to see a real challenge in our health care systems over the course of the next three to eight weeks. And what really is challenging is, on top of that, we can expect 10 to 30% of healthcare workers to get infected during that time,” he said.

The variant would not discriminate by state lines, Osterholm said.

“Instead of seeing the regional surges we were seeing with Delta — much of the West right now is very low level with Delta, parts of the South — I think Omicron is going to be a national viral blizzard,” he said.

Nearly 73% of Americans have received at least one vaccine dose, 61.5% are fully vaccinated and 29.8% of those fully vaccinated have received a booster, according to CDC figures.

Osterholm stressed that people should focus on getting optimal protection from the virus with three doses of vaccine.

“Right now we have a lot of people in this country who have bought some protection but will it be enough to actually avoid serious illness with Omicron? We don’t know.”

Osterholm said it was concerning that just 30% of vaccinated Americans had received a third dose and that it takes seven to 14 days for immunity to really pick up following a booster shot.

“Well, that takes us into the New Year. Takes us right through the holiday season and right into the heart of the Omicron, what I call, ‘blizzard.’ So it’s not looking good. It’s a real perfect storm, unfortunately, of events,”he said.

President Biden will “announce additional steps” in the fight against Covid-19 during his planned remarks on Tuesday, the White House said, but he won’t necessarily talk about additional restrictions in the face of rising cases.

States prepare for Omicron

Some states are already overwhelmed.

The Army is being deployed to help fight Covid in Indiana and Wisconsin.

Two 20-person teams consisting of medical personnel will be deployed to assist civilian hospitals in the two states, US Army Northern Command announced Monday.

In Ohio, Dr. Brook Watts, chief medical officer of community and public health at MetroHealth System in Cleveland, told CNN that Northeast Ohio is in crisis.

“I think the health systems, together, said it best this weekend. When we took out a joint ad with all the hospitals in our region and it said one word, it said ‘help.’ It said help because our hospitals are filled with patients with Covid and we’re struggling,” she said Monday.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said Monday that all Americans needed to play their part in the fight against Covid.

“It has nothing to do with freedom, it has to do with protecting yourself and your family from a potentially deadly disease that has killed already over 800,000 Americans, but also relinquishing your societal responsibility to be part of the solution, instead of part of the problem,” Fauci told the National Press Club Headliners Virtual Newsmaker event.

Unvaccinated people face a 10 times greater risk of testing positive and 20 times greater risk of dying from Covid-19 than fully vaccinated people who have also received a booster do, according to data published recently by the CDC.

Compared to fully vaccinated people yet to receive a third dose, unvaccinated people face a five times greater risk of testing positive for Covid-19 and 14 times greater risk of dying, according to the CDC assessment of data through October.

Cases have also been surging in New York State, which saw a nearly threefold increase in one week, according to data made available by Gov. Kathy Hochul on Monday.

And in New York City, officials said they were working to reinstate extra testing capacity.

In Washington, DC — which has been experiencing its highest daily coronavirus case count since the start of the pandemic — Mayor Muriel Bowser announced the indoor mask mandate will be reinstated starting at 6 a.m. Tuesday going through January 31.

In Boston, Mayor Michelle Wu announced the city would be requiring proof of Covid-19 vaccination for indoor dining, fitness venues, theaters and arenas.

The mandate will apply to both patrons and employees, and will come online in phases. Single doses of vaccine will be required by January 15, with second doses becoming required by February 15.

How parents can protect their children

Dr. Dimitri Christakis, Editor in Chief of JAMA Pediatrics, told CNN on Monday that the situation with Omicron was serious “but not dire”for children.

“From the data we have available so far it still seems that Omicron doesn’t cause serious illness in children and the good news is that children over five can get vaccinated and vaccination does proffer a significant amount of protection,” he said.

But Christakis said children aged under 5 could not yet be vaccinated and needed to be protected from the virus and that as case numbers went up with the more transmissible variant, so would the numbers of children suffering serious illness.

He advocated giving children as normal an experience as possible in a safe environment.

The-CNN-Wire™ & © 2021 Cable News Network, Inc., a Time Warner Company. All rights reserved.

Join our Newsletter for the latest news right to your inbox