As omicron becomes the dominant variant in the United States, National Institute of Allergy and Infectious Diseases Director Anthony Fauci and CDC Director Rochelle Walensky warn that it will likely lead to a record number of cases and overwhelm hospitals yet again.

The omicron variant: The 'good,' 'bad,' and 'ugly' scenarios

Experts warn that hospitals will be overwhelmed

According to the World Health Organization (WHO), the omicron variant has been detected in 89 countries and has a "substantial growth advantage" over delta—doubling every 1.5 to 3 days in areas with community spread.

"Omicron is spreading rapidly in countries with high levels of population immunity," WHO said. "Given currently available data, it is likely that omicron will outpace delta where community transmission occurs."

And as omicron continues to spread in the United States, several health experts are warning that the country will likely see record case numbers in the next few weeks. Rochelle Walensky noted that delta continues to "circulate widely," but "omicron is increasing rapidly and we expect it to become the dominant strain in the United States ... in the coming weeks." Anthony Fauci added that omicron "is the most transmissible" variant in circulation.

Separately, Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said the omicron variant will likely lead to millions of new infections, on top of those caused by the delta variant.

"We're really just about to experience a viral blizzard," Osterholm said. "In the next three to eight weeks, we're going to see millions of Americans … infected with this virus, and that will be overlaid on top of delta, and we're not yet sure exactly how that's going to work out."

A look at different scenarios

Although it is still not clear how the omicron variant will affect the trajectory of the pandemic, researchers are currently developing computer models to predict potential scenarios for the next few months.

One of the first omicron-related models to be released is from the UT Covid-19 Modeling Consortium at the University of Texas at Austin, NPR reports. The group developed 16 potential scenarios for omicron and accounted for "how quickly [omicron] spreads, how easily it evades immunity and how quickly we're able to roll out booster shots," according to Lauren Ancel Meyers, the consortium's director.

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Under the most optimistic scenario, omicron only partially evades immunity, does not make people sicker than delta, and booster uptake significantly increases. In this situation, the modelers predict the omicron wave would peak around the middle of January at around 189,069 cases a day, around double what they are now. But hospitalizations and deaths would increase at a lower rate. Under this scenario, "omicron would lead to only a few thousand more hospitalizations and few hundred more deaths each day—10,538 hospitalizations and 1,412 deaths on average."

Myers added that, in this optimistic scenario, omicron is "just sort of a little bump. It's not a catastrophic surge that overwhelms our hospitals and leads to record number of deaths."

However, in the most pessimistic scenario, omicron is extremely adept at evading immunity, makes people sicker than delta, and booster uptake remains relatively low—leading to significantly more cases, hospitalizations, and deaths. In this situation, cases are expected to rise to an average of 500,000 a day, with hospitalizations increasing to 29,812, and deaths increasing to 3,876.

"The most pessimistic scenarios are scary," Meyers said. "And we need to sort of equip ourselves to make changes—change policies, encourage more cautionary behavior—if and when we start to see hospitalizations tick up in this country."

According to CDC, omicron made up around 13% of all Covid-19 cases in the country the week of Dec. 11. But some areas, such as New York and New Jersey, saw significantly higher case rates—a trend that will likely become more common in other states in the coming weeks.

New York in particular has seen a significant rise in cases, leading some restaurants to close and colleges to cancel events, Axios reports. According to the New York Times, New York City on Saturday reported 21,908 new Covid-19 cases, surpassing its previous record of 19,942 cases in January. In addition, Tompkins County, which is home to Ithaca College and Cornell University, saw Covid-19 cases increase by more than 640% over the last two weeks.

But so far, New York hospitals aren't seeing the same surge in hospitalizations that overwhelmed EDs earlier in the pandemic, the Associated Press reports. Fritz François, the chief of hospital operations for NYU Langone Health, says that "we're actually seeing something different" than previous surges.

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At this point, Covid-19 admissions have not yet dramatically increased with the increasing case load in the area. In addition, Eric Legome, who oversees two of Mount Sinai Health System's EDs, said Covid patients' symptoms and treatments seem less severe. "We’re seeing a lot more treat-and-release" patients than in earlier waves, he said. He also noted many are looking for tests, help with mild or moderate symptoms, or antibody treatments, but very few require oxygen or a hospital stay.

What we’ve seen in South Africa—and what that may mean for the U.S.

While omicron's severity is still unknown, recent data from South Africa suggests that the variant may lead to less severe disease—meaning people are less likely to be hospitalized and recover more quickly from illness, NPR reports.

However, several experts warn that South Africa's experience with omicron may not reflect what the United States ultimately experiences with the variant. Although vaccination rates remain low in South Africa, most of its population has a high level of natural immunity from infection, which may be why the country is seeing milder cases from omicron.

In comparison, scientists estimate that a minimum of 20% of the U.S. population—around 66 million people—have no immunity against Covid-19 from vaccination or prior infection, potentially putting them at significant risk of severe disease from omicron.

In addition, many experts have said that even if omicron results in milder cases, its rapid spread could still lead to a significant number of cases that could overwhelm hospitals, particularly those already struggling with a delta surge in cases.

"When you have so many infections, even if it is less severe, that overcomes this slight to moderate diminution in severity," Fauci said. "Our hospitals, if things look like they are looking now, in the next week or two are going to be very stressed with people."

He added that omicron would likely lead to record numbers of Covid-19 cases. "It is going to be a tough few weeks to months, as we get deeper into the winter," Fauci said.

To mitigate the potential risks of an omicron surge this winter, several health officials and organizations, including the American Hospital Association, American Medical Association, and American Nurses Association, have encouraged all eligible Americans to get vaccinated and receive a booster shot.

"This is not a moment to panic, because we know how to protect people and we have the tools to do it," said Jeff Zients, White House Covid-19 response coordinator. "The more people get vaccinated, the less severe this omicron outbreak will be." (Doherty, Axios, 12/18; Macias, CNBC, 12/16; Firth, MedPage Today, 12/17; Caldwell, CNN/CBS58, 12/17; Stein, "Shots," NPR, 12/17; Levenson, New York Times, 12/18; Wernau/Patel, Wall Street Journal, 12/17; Owens, Axios, 12/17; Doucleff/Wood, "Goats and Soda," NPR, 12/17; Friedman/Abbott, Wall Street Journal, 12/19; Saric, Axios, 12/19; AHA News, 12/17; Peltz, Associated Press, 12/18)