New York City officials issued an advisory Monday "strongly" recommending that people mask up indoors regardless of vaccination status to curb the spread of the newly-discovered Omicron variant.

Why it matters: Dave Chokshi, commissioner of the New York City Department of Health and Mental Hygiene, announced the advisory in response to concerns of the new strain's potential implications.

A federal court in Missouri has blocked the Biden administration from enforcing a coronavirus vaccine mandate for health care workers at federally funded facilities in 10 states.

Why it matters: Monday's decision is the first victory for opponents of the rule, which requires health care workers to get vaccinated by Jan. 4, 2022. The case is one of four lawsuits challenging the Centers for Medicare & Medicaid Services' (CMS) rule and argues that the mandate will exacerbate staffing shortages.

The Centers for Disease Control and Prevention (CDC) on Monday strengthened its previous recommendation for booster shots, saying that everyone 18 and older "should" receive a booster dose.

Why it matters: Last month, CDC director Rochelle Walensky accepted a key advisory committee's recommendation that adults "may" get the shot. The slight, but strengthened, change in wording comes amid the emergence of the Omicron coronavirus variant.

President Biden on Monday said that the new coronavirus variant, Omicron, is "a cause for concern, not a cause for panic."

Driving the news: Biden said later this week the administration will be releasing a strategy on how "we're going to fight COVID this winter. Not with shutdowns or lockdowns, but with more widespread vaccinations, boosters, testing and more."

1. Health: WHO says Omicron poses "very high" risk — Fauci says Omicron variant will "inevitably" be found in U.S. — U.S. restricts air travel from 8 countries over Omicron concerns.
2. Politics: Biden says fight against Omicron won't include "shutdowns or lockdowns."
3. States: New York declares state of emergency amid concerns over Omicron.
4. World: Omicron adds urgency to vaccinating world — WHO warns against travel bans on southern African countries — First North American Omicron cases identified in Canada.
5. Variant tracker: Where different strains are spreading.

The Transportation Security Administration screened 2,451,300 people at airports across the U.S. on Sunday, making it the busiest day for air travel since the beginning of the pandemic.

Driving the news: Nearly 20.9 million passengers passed through TSA checkpoints from Nov. 19 through Nov. 28, more than double the number of air travelers screened during the same period last year, TSA said.

The World Health Organization said Monday in a new risk assessment that it believes the COVID-19 Omicron variant poses a "very high" risk to the globe because it may be more transmissible than other strains of the virus.

Why it matters: Though the WHO acknowledged there are still many uncertainties associated with the variant, the agency said it believes the likelihood of potential further spread of Omicron around the world is "high."

An Ohio man appears to have been cured of his Type 1 diabetes after participating in an early-stage clinical trial of a stem cell treatment by Vertex Pharmaceuticals, the New York Times reports.

Why it matters: If ultimately successful, the development could offer hope to millions of Americans who suffer the life-altering symptoms of the disease.

Box office ticket sales over the Thanksgiving holiday show that consumer confidence in moviegoing is slowly improving but not enough to bring the struggling theater industry back to pre-pandemic levels anytime soon, if ever.

Why it matters: "We may have to temper expectations a bit" for next year, said Comscore senior media analyst Paul Dergarabedian.

The emergence of the Omicron variant is bringing new urgency to global vaccination efforts.

Why it matters: New variants can emerge anywhere, and can spread everywhere. Getting doses to the developing world — and getting those doses into people's arms — is essential, and that effort has so far been lagging.

A bipartisan group of U.S. House members chided the Biden administration for repealing a rule that would have required Medicare to pay for any medical device deemed a "breakthrough" by the FDA.

The big picture: Medical device manufacturers really wanted the rule enacted, in part, because it would have led to higher sales. Now many members of Congress who receive sizable campaign donations from the industry want the federal government to revive the rule.

The first two cases of the new Omicron variant have been detected in North America, the Canadian government announced Sunday evening.

Driving the news: The World Health Organization has named Omicron a "variant of concern," but cautioned earlier on Sunday that it is not yet clear whether it's more transmissible than other strains of COVID-19.

The World Health Organization called on countries Sunday not to impose travel bans on southern African nations amid concerns over the COVID-19 Omicron variant.

Why it matters: The U.S. and countries in Europe and the Asia-Pacific announced travel restrictions in response to Omicron, which was first detected in South Africa. It's since been identified in several European countries, Canada, Israel, Australia and Hong Kong. The WHO noted in a statement that only two southern African nations have detected the new strain.