COVID updates: Secretary of Defense Lloyd Austin tests positive

Officials from Michigan's Department of Health and Human Services sent a letter to schools across the state urging them to either postpone large gatherings or make them virtual.

"Large gatherings (involving 100 or more people) should be held using remote technology or postponed, if not essential. Large gatherings would include events with large numbers of people from multiple households such as conferences or meetings, sporting events, and concerts," the letter read.

The state also urged schools to require masks for everyone who enters school buildings and to test students regularly.

-ABC News' Will McDuffie

More than 90,000 Americans are currently hospitalized with COVID-19, which is double the number since November, according to a memo from the U.S. Department of Health and Human Services.

On average, more than 9,400 Americans are being admitted to the hospital with COVID-19 every day, a 20% increase compared to the last week, HHS said.

The hospitalization numbers are still roughly three-quarters of the same period in 2020, the data showed.

-ABC News' Arielle Mitropoulos and Josh Margolin

Mondli Gungubele, the South Africa's Minister in the Presidency, tweeted some promising updates on the country's current COVID-19 surge.

The country's health department saw a 29.7% decrease in the number of new cases detected in the week ending Dec. 25 compared to the previous week.

"All indicators suggest the country may have passed the peak of the fourth wave at a national level," the minister tweeted.

South Africa was one of the first nations to record the omicron COVID-19 variant and saw cases spike in late November.

The health department said that while the omicron variant is highly transmissible, the country's hospitalization rates were lower than in previous waves.

South African officials announced they will lift several restrictions, including its curfew and crowd limits for indoor and outdoor activities.

-ABC News' Christine Theodorou

The Centers for Disease Control and Prevention (CDC) warned Americans to avoid cruises regardless of COVID vaccination status.

On Thursday, the CDC raised the health notice from a level 3 to a level 4, which is the highest level.

"Since the identification of the omicron variant, there has been an increase in the number of COVID-19 cases among cruise passengers and crew reported to CDC," the agency wrote. "Additionally, there has been an increase in the number of cruise ships meeting the COVID-19 case threshold for CDC investigation."

More than 80 cruise ships are currently being investigated or observed by the CDC after reports of COVID outbreaks on board.

In response, the Cruise Lines International Association -- the largest cruise trade association -- called the CDC's new warning "particularly perplexing" and said cases on ships "consistently make up a very slim minority of the total population onboard."

ABC News' Alexandra Faul, Mina Kaji and Sam Sweeney