Harvard University is shifting to remote learning for the first three weeks of January due to a "rapid" rise in COVID-19 cases locally, school officials announced Saturday.

"Please know that we do not take this step lightly," school leaders said in an update to students. "It is prompted by the rapid rise in COVID-19 cases locally and across the country, as well as the growing presence of the highly transmissible Omicron variant." 

Only students with previous authorization will be allowed to remain on campus. Some programs, like essential in-person laboratory and patient-centered work, will continue as normal, the school said.

"We are planning a return to more robust on-campus activities later in January, public health conditions permitting," the school officials said. 

Several universities, including Princeton, NYU and Cornell, have shifted final exams remote and canceled events in recent days due to spikes in COVID-19 cases.

-ABC News' Arielle Mitropoulos

Enforcement of the Biden administration's vaccine-or-test mandate for private companies with more 100 employees will be delayed by a month, officials said.

The Labor Department’s Occupational Safety and Health Administration announced the change Saturday, a day after a federal appeals court lifted a stay on the rule, allowing it to proceed. 

Previously, the mandate required companies to enforce masks among unvaccinated employees beginning Dec. 6, and either see proof of vaccination or begin testing workers weekly by Jan. 4. 

The new deadlines for compliance are now Jan. 10 and Feb. 9, respectively, OSHA said.

-ABC News' Anne Flaherty

Nearly 22,000 positive COVID-19 test results were reported in New York state in the last 24 hours, according to Gov. Kathy Hochul's office -- breaking a single-day record set the day before. 

The 21,908 positive COVID-19 test results are out of 290,930 results reported -- for a 7.53% positivity rate.

Demand for testing also continues to rise, with about 27,000 more people getting tested on Friday.

"This is not like the beginning of the pandemic. We are prepared for the winter surge because we have the tools at our disposal," Hochul said in a statement. "Getting vaccinated, getting the booster and wearing a mask are critical to avoiding getting seriously ill from COVID-19, so don't take a chance."

-ABC News' Joshua Hoyos

President Joe Biden will deliver remarks this Tuesday on the country's fight against COVID-19 and "announce new steps" the administration will take amid the growing spread of the omicron variant, White House officials said.

The president will address steps the administration is taking "to help communities in need of assistance, while also issuing a stark warning of what the winter will look like for Americans that choose to remain unvaccinated," White House press secretary Jen Psaki said on Twitter Saturday afternoon.

The speech will come as millions of Americans prepare to travel and gather for the holidays, and as concerns about the omicron variant continue in the U.S. and around the world. 

-ABC News' Molly Nagle