The Omicron variant is currently causing about 13 percent of new COVID-19 cases in New York and New Jersey, according to .

Nationwide, the variant has gone from causing 0.4 percent of new cases in the week ending December 4, to 2.9 percent of cases in the week ending December 11 - a seven-fold increase. 

CDC Director Dr Rochelle Walensky that the variant is 'more transmissible' and 'rapidly becoming the more predominant strain' in other countries.

As cases increase in the U.S. - with 120,000 new cases reported daily - experts have advised Americans to get vaccinated, utilize tests, and mask up in indoor public spaces. Total US cases have now passed the 50.1 million mark, with around 800,000 killed by the virus so far. 

The highly contagious Omicron variant was first detected in South Africa and Botswana in late November.

Since then, it's caused a major case surge in South Africa, overtaking the Delta variant.

The variant has also been identified around the world: as of Tuesday, have been detected in 77 countries.

That includes more than 180 cases in the U.S., with the variant identified in 35 states.

At a press briefing last week, Walensky said the Delta variant remained the country's top concern, as it was causing over 99 percent of cases in the U.S.

But new estimates from the CDC - released Tuesday morning - indicate that the Omicron variant is spreading rapidly in the U.S., and may overtake Delta within weeks.

Omicron caused 2.9 percent of new Covid cases nationwide, in the week ending December 11.

That's a six-fold increase from the previous week, in which Omicron caused 0.4 percent of new Covid cases.

The CDC's updated data also indicate that Omicron was already spreading in the U.S. by Thanksgiving, causing 0.1 percent of cases nationwide in the week ending November 27.

'It is more transmissible, and we're seeing that in other countries as well, that it's rapidly becoming the more predominant strain, but I want to emphasize that we have the tools now,' said CDC Director Rochelle Walensky of the new variant on TODAY Tuesday morning.

'The science is still evolving, it's still early, but what we're seeing in some of these other countries is doubling times of about every two days or so, so really rapid increase in the amount of Omicron that's out there,' she said.

Omicron spread is particularly high in the New York and New Jersey area: in this region, Omicron caused 13 percent of cases in the last week.

Midwest states Iowa, Kansas, Missouri, and Nebraska have the next-highest share of Omicron cases, at 3.9 percent.

They're followed by 2.7 percent, in Arkansas, Louisiana, New Mexico, Oklahoma, and Texas.

In the remainder of the country, under 2.5 percent of new cases were caused by Omicron, with several regions under one percent, according to the CDC's estimates.

Overall Covid cases have sharply increased in New York in recent weeks, from a daily average of 7,600 new cases on November 29 to a daily average of 10,500 on December 13.

That's an increase of about 40 percent in the two weeks since Thanksgiving.

Meanwhile in New Jersey, Covid cases have increased by almost 60 percent in the past two weeks - from 2,700 daily new cases on November 29 to 4,300 on December 13.

Both states are seeing increases in Covid hospitalizations as well, with 3,300 patients currently hospitalized in New York and 1,400 in New Jersey.

Omicron spread in the New York City area may have been , a convention held in lower Manhattan between November 19 and 21.

A convention attendee who traveled to NYC from Minnesota was the one of the first Omicron cases detected in the U.S.

Since then, several other Omicron cases have been connected to the convention, which drew over 50,000 attendees.

The CDC is currently investigating the event as a potential superspreader event.

Data from South Africa, the U.K., https://com-x.life/ and other countries have demonstrated that Omicron is highly transmissible and able to compete with Delta.

Early studies on vaccine effectiveness have found that existing Covid vaccines protect well against severe disease and death from Omicron, but are less effective against infection.

Data from South Africa - including a new study released Tuesday - suggest that Omicron causes more mild symptoms than past variants, though the apparent trend may be because many South Africans have some Covid protection from vaccination or prior infection.

'We're starting to see some early data that is demonstrating some decreased severity,' Walensky said on the TODAY show.

However, she said, if a lot more people get infected with Omicron - even if a lower share of those people have severe symptoms - the wave of cases could still lead to a high number of serious cases.

'The best way to protect yourself against COVID is to not get it in the first place, and that is to get vaccinated and boosted,' Walensky said.

For those who do have symptoms, the Pfizer antiviral pill currently under consideration for FDA authorization could be 'another great tool' for preventing hospitalization.

As the holiday season continues, experts recommend testing before indoor gatherings and masking up in indoor public spaces.