Omicron updates: COVID-19 cases could double in New York City

The United Kingdom raised the COVID-19 alert level on Sunday, citing a rapid increase in cases of the omicron variant. 

The U.K. has detected 3,137 omicron cases so far, according to the GISAID tracker.

In an address to the nation Sunday, British Prime Minister Boris Johnson said the data on the severity of the new variant would become more apparent in the coming weeks. Still, at this stage, Johnson said early evidence shows that omicron is spreading much faster than the highly contagious delta variant.

Vaccine protection against symptomatic disease from omicron is reduced and hospitalizations from the new variant are already occurring. Cases and hospitalizations are likely to increase rapidly, Johnson warned.

In an effort to battle the "tidal wave of omicron" and avoid imposing further restrictions, the prime minister announced his government will begin rolling out 1 million booster doses of the COVID-19 vaccine per day across all four nations of the U.K. -- England, Scotland, Wales and Northern Ireland. He vowed that everyone over the age of 18 will have the opportunity to receive a booster shot before the New Year. The British Army will be deployed to facilitate and accelerate the emergency rollout, according to Johnson.

-ABC News' Christine Theodorou and Mike Trew

Nearly a month after imposing additional rules to fight rising COVID-19 infections, Austrian authorities will now allow vaccinated people to participate in public life starting Sunday. 

Lockdown restrictions will still apply to unvaccinated individuals.

But Austria's tough response to rising COVID infections doesn't end there. The health minister, Wolfgang Mueckstein, announced that starting Feb. 1 and going through Jan. 2024, COVID vaccines will be mandatory, for all residents aged 14 and over

At the end of each quarter, residents who remain unvaccinated face fines up to $4,074.

The mandate, which still needs to be approved by parliament, will include exemptions for women who are pregnant, children under the age of 14 and people who cannot be vaccinated for health reasons.

-ABC News' Christine Theodorou

More than 50 million Americans have now received a COVID-19 booster shot, according to newly updated federal data.

More than half of fully vaccinated people 65 years and older have received a booster.

On average, about 2.03 million total shots are being administered each day, the data shows. More than half -- 1.1 million -- are booster doses.

-ABC News' Arielle Mitropoulos

The PolicyLab at Children's Hospital of Philadelphia predicts "significant" case growth across much of the U.S. over the next four weeks.

According to forecasters, large metropolitan areas, particularly in the Northeast, are seeing significant case growth following Thanksgiving. 

Cases in the New York City area are expected to at least double through December, the forecasters said. 

Metropolitan areas in New Jersey, Delaware and North Carolina are expected to see a rapid case increase, forecasters said. 

The forecasters also noted a "sudden" increase in cases in Florida in the last two weeks. 

-ABC News' Arielle Mitropoulos