A federal appeals court reinstated the Biden administration's nationwide workplace vaccine mandate Friday.

The Sixth Circuit Court of Appeals dissolved the stay issued by the Fifth Circuit last month on the rule, which would require employees at private companies with over 100 workers to get vaccinated or tested regularly.

The mandate "is an important step in curtailing the transmission of a deadly virus that has killed over 800,000 people in the United States, brought our healthcare system to its knees, forced businesses to shut down for months on end, and cost hundreds of thousands of workers their jobs," Judge Jane Stranch wrote in the opinion.

The rule, which was set to go into effect on Jan. 4, 2022, had been put on hold by the Fifth Circuit after it ruled that the Labor Department’s Occupational Safety and Health Administration didn’t have the legal authority to impose such a requirement on private businesses.

The Labor Department had previously said it won’t move forward with enforcing its workplace mandate until the matter was resolved in court.

Arkansas Attorney General Leslie Rutledge said Friday she plans to ask the U.S. Supreme Court to block the order.

-ABC News' Benjamin Siu and Anne Flaherty

The omicron variant could spread two to three times faster than delta, according to a new report from the Imperial College London COVID-19 response team.

The study, which has not yet been peer-reviewed, also estimated that the risk of being reinfected with omicron is more than five times higher than that of delta.

Data could change as more information on omicron's spread is gathered, though the study offers an early indication of how much more transmissible the new variant is compared to delta.

-ABC News' Cheyenne Haslett, Dr. John Brownstein and Sony Salzman

Due to a "substantial increase in cases across the league," the NFL announced that several weekend games have been pushed back.

Saturday's game between the Las Vegas Raiders and Cleveland Browns has been moved from Saturday to Monday.

The Washington Football Team vs. Philadelphia Eagles matchup and Seattle Seahawks-Los Angeles Rams game have both been moved from Sunday to Tuesday.

New York state reported 21,027 cases Thursday, setting a new single-day high, Gov. Kathy Hochul's office said.

"The winter surge in COVID-19 cases is a reminder that the pandemic is not over yet and we must take extra care to keep ourselves and each other safe," Hochul said in a statement. "The vaccine is still our best weapon to defeat the virus."

-ABC News' Josh Hoyos

France announced Thursday that it will ban non-essential travel to and from the United Kingdom due to the country's surge in cases of the omicron variant.

Starting Saturday, France will require people to have "a compelling reason" to travel between the two countries. Travel for tourism or work will not be allowed. French citizens, however, can return to France, according to a statement from the French prime minister's office.

All travelers from the U.K. will be required to show proof of a negative COVID-19 test taken less than 24 hours before departure. Upon arrival in France, they must self-isolate for a week, but that period can be ended after 48 hours if they test negative for COVID-19 again.

The new rules apply to people regardless of their vaccination status.

"Faced with the extremely rapid spread of the Omicron variant in the United Kingdom, the Government has chosen to reinstate the need for an essential reason for travel from and to the United Kingdom, and to strengthen the requirement for tests on departure and arrival," the French prime minister's office said in the statement Thursday. "The Government is also calling on travelers who had planned to visit the United Kingdom to postpone their trip."