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The study, which has not yet been peer-reviewed, also estimated that the risk of being reinfected with omicron is more than five times higher than that of delta.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

Indonesia announced Thursday its first confirmed case of the omicron variant.

The case was detected in a janitor who works at the COVID-19 Emergency Hospital of Kemayoran Athletes Village in Jakarta, according to a statement from Indonesian Health Minister Budi Gunadi Sadikin.

The hospital's cleaning staff are routinely tested and the results for three people were positive for COVID-19 on Dec. 10. Those samples were then sent to a genome sequencing lab, which identified the omicron variant in one of the samples on Wednesday, according to the statement.

Indonesia's Ministry of Health has also identified probable cases of omicron among five travelers who were in quarantine -- two Indonesian citizens who had just returned from the United Kingdom and the United States, and three foreigners from China. Their test samples are being sequenced and the results will be known in a few days, according to the statement.

The health minister urged Indonesians "not to panic and to remain calm," and to get vaccinated against COVID-19 if they haven't already.

"The arrival of new variants from abroad, which we identified in quarantine, shows that our defense system against the arrival of new variants is quite good, we need to strengthen it," Sadikin said. "So it's normal to stay 10 days in quarantine. The goal is not to make it difficult for people who came, but to protect the people of Indonesia."