Massachusetts Gov. Charlie Baker said he's activating 500 more National Guard members to support the state's strained health care system.

Baker had activated 250 National Guard members when students returned to classrooms in the fall to help with school transportation, ABC Boston affiliate WCVB reported.

In Maine, Gov. Janet Mills is activating up to 169 National Guard members to help overrun hospitals, ABC affiliate WMTW reported. Maine hit a hospitalization record Monday with over 400 COVID-19 patients in hospitals, according to WMTW.

New Orleans will reinstate its indoor mask mandate beginning Wednesday as the city gears up for Mardi Gras celebrations.

Masks will be required in restaurants, bars, gyms, entertainment venues and public transportation.

About 64.6% of New Orleans residents are fully vaccinated, according to the city.

People 5 and older must show proof of vaccination or a negative test to access indoor restaurants, bars, entertainment venues, bowling alleys, indoor playgrounds, arcades and similar settings.

Omicron is estimated to account for 98.3% of new cases in the U.S. as of Jan. 8, according to new data released by CDC Tuesday. (These figures are calculated using modeling and may not be exact.)

Delta now accounts for only 1.7% of new cases nationally, forecasters estimate.

In three areas of the country -- the deep South, the Southeast and the New York/New Jersey region -- omicron is estimated to account for more than 99% of new cases.

In early December, omicron was estimated to account for just 0.6% of all new cases.

-ABC News' Arielle Mitropoulos

The White House has been limiting its in-person gatherings to 30 people "over the last several weeks" due to the omicron surge, White House press secretary Jen Psaki said.

“We wear masks in the West Wing at all times, including in your office, unless you're in your office alone,” Psaki said.

-ABC News' Ben Gittleson

Russian officials are warning that an omicron-fueled wave of COVID-19 infections will soon hit, amid fears about how deadly a surge of the highly contagious variant -- even if milder -- might be in a country with a low vaccination rate.

Russian Deputy Prime Minister Tatiana Golikova, who is overseeing the COVID-19 response, and Moscow Mayor Sergey Sobyanin said Wednesday that the situation could be "more critical" than previous waves of infections in Russia -- a worrying prospect since earlier waves led to a high number of deaths.

Russia has reported more than 312,000 fatalities from COVID-19 since the start of the pandemic, according to data compiled by Johns Hopkins University. However, the country registered just under 1 million excess deaths in 2021.

The Russian government has said the country will soon see six-figure daily cases. Less than 50% of Russians are fully vaccinated against COVID-19, amid widespread reluctance across the nation.

Russian President Vladimir Putin, who has largely tried to downplay the scale of his country's COVID-19 outbreak, warned Wednesday of the imminent increase in infections. Putin said Russia is "on the threshold of possible new outbreaks."

Meanwhile, Russian Health Minister Mikhail Murashko said the country is at a "turning point," which will decide how bad the wave will be. Russian authorities are calling for people to take precautions and observe social distancing measures. However, there are relatively few restrictions in most parts of the country.

Denis Logunov, deputy director of Russia's Gamaleya National Center of Epidemiology and Microbiology, said Tuesday that the nationwide number of omicron cases is expected to rise considerably in late January and early February. The World Health Organization's regional director for Europe, Dr. Hans Kluge, also warned Tuesday that omicron is expected to infect more than half of Europe's population within the next two months.

-ABC News' Patrick Reevell