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

California is reinstating an indoor mask mandate from Dec. 15 to Jan. 15.

Half of the state is already under a mask mandate per local rules, according to California Health and Human Services Secretary Mark Ghaly.

California is also tightening restrictions on unvaccinated people at large events. At events with more than 1,000 people, anyone who isn’t vaccinated must show proof of a negative antigen test within 24 hours or a negative PCR test within 48 hours.

State officials also recommend that travelers get tested three to five days before arriving in California.

-ABC News' Matt Fuhrman

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."