COVID-19 updates: Elizabeth Warren tests positive

The Centers for Disease Control and Prevention on Friday endorsed a practice in schools called “test-to-stay,” which allows unvaccinated kids and staff to test instead of quarantine after being exposed to COVID-19.

The CDC says the practice can be employed in addition to other mitigation measures, such as vaccination and at least 3-feet of physical distance among students wearing masks.

The new guidance follows two studies out of Los Angeles County, California, and Lake County, Illinois. Both studies found no significant transmission in school when test-to-stay was used.

The studies were conducted before the omicron variant was detected in the U.S.

-ABC News' Anne Flaherty

In Wisconsin, only 4% of ICU beds are available.

"This is getting really scary," Dr. Jamie Hess, an emergency physician at the University of Wisconsin, told ABC News.

"We're really reaching a crisis point where we have more patients to take care of then we have beds in the hospital or staff to care for them," Hess said.

Michigan has been struggling through a similar surge for nearly three months, with the state reporting more than 6,500 new cases each day. On average, more than 500 patients are being admitted to hospitals each day.

"Where we are right now feels a lot like the first surge back in March of 2020," Erin Dicks, a nurse manager at MICU Henry Ford Hospital, told ABC News. "We don't have enough beds to be able to manage this."

Dicks said so many patients are young.

"I think one of the biggest frustrating pieces for my staff is that they look at this as, this is preventable -- people don't have to die here," Dicks said.

-ABC News' Arielle Mitropoulos

Harvard University will require boosters for all eligible members of the community, school officials said Thursday.

Earlier this week, Harvard warned of an increase in cases, saying the rise can be attributed to social events following the Thanksgiving break.

Omicron is likely already on campus, university officials added.

Harvard joins a growing list of colleges and universities moving to require third doses next semester for those eligible. Other schools include Stanford, NYU, University of Notre Dame, Syracuse, Smith College and Wellesley College.

-ABC News' Arielle Mitropoulos

In Illinois, 11,858 new cases were reported on Thursday -- the highest daily case number of all of 2021, ABC Chicago station WLS reported, citing state health officials.

Illinois confirmed its second omicron case Wednesday, detected in a suburban Chicago resident. That person is asymptomatic and vaccinated, WLS reported.