By Joseph Ax and Barbara Goldberg

(Reuters) – Two years into the coronavirus pandemic, the United States is confronting another dark winter, with the red-hot Omicron variant threatening to further inflame an already dangerous surge of cases.

Hospitalizations for COVID-19 have jumped 45% over the last month, and cases have increased 40% to a seven-day average of 123,000 new infections a day, according to a Reuters tally.

Pfizer Inc, one of the chief vaccine makers, on Friday predicted the pandemic would last until 2024 and said a lower-dose version of its vaccine for children ages 2 to 4 generated a weaker-than-expected immune response, which could delay authorization.

The Omicron variant appears to be far more transmissible than previous iterations of the virus and more agile in evading immune defenses, according to early studies.

Public health officials say it is likely to become the dominant variant in the country, following fast-moving spreads in countries such as South Africa and the United Kingdom, and could strain hospitals still struggling to contain this summer’s Delta variant surge.

“GET BOOSTED NOW. Tidal wave of Omicron likely coming to a hospital near you soon,” Dr. Tom Frieden, former chief of the Centers for Disease Control and Prevention (CDC), posted on Twitter.

Preliminary data in South Africa suggests Omicron leads to milder illness than the Delta variant, which is still driving much of the current wave. But a British study released on Friday found no difference in severity between the two variants.

Either way, Omicron’s extraordinary level of infectiousness means it could cause many additional deaths, the top U.S. infectious disease expert, Dr. Anthony Fauci, said on Friday.

“When you have a larger number of people getting infected, the total amount of hospitalizations is going to be more. That’s just simple math,” Fauci told CNBC.

Fauci also said officials are discussing whether to redefine what it means to be “fully vaccinated” to include booster shots, which according to early studies significantly improve protection against severe cases from the Omicron variant. President Joe Biden warned on Thursday that unvaccinated Americans face “severe illness and death” in coming months.

The latest surge is creating yet another round of disruptions to daily life, though widespread lockdowns have not been put in place. Several states have hit alarming levels of cases and hospitalizations.

Exhausted hospital workers in Ohio who are in their 22nd month of pandemic response will be getting some help starting on Monday from 1,050 National Guard troops – including 150 nurses, emergency medical technicians and others with medical training – being deployed to hospitals around the state, Governor Mike DeWine told a news conference on Friday.

In New York City, Radio City Music Hall announced that Friday’s four performances of the Rockettes’ iconic Christmas show were canceled due to “breakthrough COVID-19 cases in the production.” Broadway shows have also canceled performances this week after outbreaks among vaccinated cast members.

Both the National Hockey League and National Basketball Association postponed games this week, and the NBA and National Football League imposed heightened COVID-19 restrictions after dozens of players tested positive.

The CDC released a new “test-to-stay” strategy on Friday that allows unvaccinated children to remain in school even if they are exposed to the virus.

The protocol is intended to replace automatic quarantines, which have required tens of thousands of students to miss school days this fall.

“If exposed children meet a certain criteria and continue to test negative, they can stay at school instead of quarantining at home,” CDC Director Dr. Rochelle Walensky told reporters.

Dr. Leana Wen, a public health professor at George Washington University, on Friday praised the test-to-stay school policy change but said implementation would still be a challenge, in part due to persistent testing shortages.

“I’m not sure how we’re able to literally implement this test-to-stay when we don’t even have enough testing for people who are symptomatic,” she told CNN.

(Reporting by Joseph Ax in Princeton, New Jersey, and Barbara Goldberg in Maplewood, New Jersey; Additional reporting by Nandita Bose, Carl O’Donnell, Susan Heavey, Caroline Humer, Mrinalika Roy, Leroy Leo and Frank Pingue; Editing by Howard Goller)