COVID-19 updates: Elizabeth Warren tests positive

China has confirmed its first case of the omicron variant on the mainland, state-run media reported Monday.

The variant was detected in a traveler from overseas who arrived in the northern Chinese port city of Tianjin on Dec. 9. The individual tested positive for COVID-19 last week and subsequent genome sequencing confirmed it was the omicron variant.

The patient, who showed no symptoms, is being treated in isolation at a hospital, according to state-run media.

At least one person has died in the United Kingdom after being infected with the omicron variant, British Prime Minister Boris Johnson said Monday.

It's the first publicly confirmed death globally from the new variant of the novel coronavirus, which was initially identified in southern Africa last month and has since spread rapidly around the world. Deaths from omicron may have already occurred in other countries but no others have been publicly confirmed yet.

Speaking to reporters during a visit to a vaccination clinic in London, Johnson said the death was a patient who had been diagnosed at a hospital but gave no further details.

"Sadly, at least one patient has now been confirmed to have died with omicron," the prime minister said. "So I think the idea that this is somehow a milder version of the virus, I think that's something we need to set on one side and just recognize the sheer pace at which it accelerates through the population. So the best thing we can do is all get our boosters."

The National Football League will require that all its vaccinated Tier 1 and 2 employees receive COVID-19 booster shots by Dec. 27, according to a memo sent to all 32 teams within the professional American football league on Monday.

This group of employees includes coaches and other employees who work closely with NFL players and help in essential league operations.

"On November 29, the CDC issued a study showing that the effectiveness of the approved COVID-19 vaccines may decrease over time and has recommended that all eligible vaccinated individuals over the age of 18 should receive a booster shot," the memo states. "Given the increased prevalence of the virus in our communities, our experts have recommended that we implement the CDC’s recommendation."

The memo came as 36 players were added to the NFLS's COVID-19 reserve list. Players are currently not required to receive boosters; but in Monday’s memo, the NFL said teams should consider making boosters available for players and their families.

"Any individual who is not currently subject to the requirement for boosters will be required to obtain the booster within 14 days of becoming eligible," the memo states.

-ABC News’ Katie Conway

The U.S. Air Force gave administrative discharges to 27 personnel who refused to get vaccinated against COVID-19 and comply with the federal government's mandate.

Over 7,000 Air Force members are unvaccinated against COVID-19, which includes about 4,500 who are waiting to see if they are eligible for religious exemption. More than 1,500 religious exemption requests have been denied and those individuals remain unvaccinated.

The Air Force has not granted a single religious exemption, according to officials.

Over 1,000 members have outright refused to get their shots.

More discharges over vaccine refusal are likely, according to an official.

-ABC News' Luis Martinez