In the United Kingdom, omicron cases are rapidly rising, leading the government to reinstate restrictions and expand booster availability to all adults—and some health experts believe the U.K.'s experience with omicron may be a preview of what the United States will see in the next few weeks.

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

Omicron spreads throughout the U.K.

Since cases of the omicron variant were first detected in the United Kingdom in late November, the variant has rapidly spread throughout country, leading to significant increases in new cases, the Wall Street Journal reports.

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According to public health officials, omicron cases in the U.K. are now doubling every two to three days, and the country may see around one million omicron infections by the end of the month. As of Sunday, the United Kingdom reported 3,137 confirmed omicron cases, up from 1,265 cases on Friday.

And U.K. Health Secretary Sajid Javid said the true number of omicron cases in the country could be much higher than the number of confirmed cases. "The number of infections is closer to 10,000," he said.

According to models developed by a panel of scientists who advise the U.K. government, omicron is most likely more transmissible than delta and can partially evade immunity through vaccination or prior infection, increasing the number of potentially susceptible people. Overall, these characteristics suggest that omicron will eventually outcompete delta, just like delta outcompeted past variants, the Journal reports.

Although the scientists who developed the models said they were optimistic that vaccines will still protect people from severe illness from omicron, the variant's increased transmissibility and partial immune evasion mean that large outbreaks could still lead to deadly surges of severe illness that overtax health care systems.

In a statement on Sunday, Prime Minister Boris Johnson said, "No-one should be in any doubt: there is a tidal wave of omicron coming." He warned omicron would become the dominant variant in London as soon as Tuesday, the Evening Standard reports.

U.K tightens restrictions

Johnson last week announced new restrictions to reduce the spread of the omicron variant, including a work-from-home order, masking requirements in indoor public areas, and proof of vaccination or a negative Covid-19 test to enter nightclubs and other venues.

In addition, senior health officials on Sunday said the U.K.'s coronavirus alert level was moved to "level 4," which means that viral transmission is high and pressure on health care services is "widespread and substantial or rising."

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"If we see even half the severity that we saw with delta then we're facing a very large number of hospitalizations and potential deaths,” said Susan Hopkins, chief medical adviser at U.K.'s Health Security Agency. She added that the government "may need to go beyond" its new restrictions to keep the omicron variant under control.

In addition to the new restrictions, the U.K. has also launched a new "Omicron Emergency Boost" initiative to offer booster doses to more people more quickly. Under the new initiative, booster eligibility was expanded to include all individuals ages 18 and older, and the interval between a second dose and a booster was shortened from six months to three months.

So far, around 22 million people in the U.K., or a third of its population, have received a booster dose of a Covid-19 vaccine, the Journal reports.

Why the U.S. should pay attention to what's happening in the U.K.

According to several experts, how omicron is currently affecting the U.K. is likely a good indication of how it will affect the United States in the next few weeks—particularly due to the country's similar vaccination rates and experiences with the delta variant. Currently, CDC reports that the omicron variant has been detected in 30 U.S. states and the District of Columbia.

"There's no way one can understand what's going on [in the United States] without knowing what's going on in the U.K. and South Africa and other places where the variant has cropped up,” said Philip Landrigan, director of the Program for Global Public Health and the Common Good at Boston College.

In addition, former FDA commissioner Scott Gottlieb said rising cases in the United Kingdom and the country's new restrictions suggest that other areas of the world, including the United States, could soon face similar experiences.

"It's deeply concerning to see the British to take this stance," Gottlieb said. "[I]f they are seeing a significant threat from omicron, I think the world should take notice of that."

"What's concerning about the U.K. for the U.S. is the U.K. has a very similar composition of immunity to the U.S.," he added. "If the U.K. has a bad experience with omicron it is a good indication we are going to be at risk as well." (Colchester/Douglas, Wall Street Journal, 12/8; Douglas, Wall Street Journal, 12/10; McDonald, Politico, 12/12; Dickson, Politico, 12/12; "Squawk Box," CNBC, 12/13; Keane/Dunne, Evening Standard, 12/13)