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

The labs shouldering much of the nation's PCR COVID-19 testing are getting slammed with demand again during omicron's surge, and now they're grappling with a new challenge: their workforces are getting hit by the virus they've been tasked with tracking.

The American Clinical Laboratory Association, the national trade association representing some of the leading clinical labs responsible for COVID diagnostics, is warning that their members' workforce is strained as more workers call out sick.

"Labs are now facing a wave of new issues brought on by a fast-spreading variant that has not spared the laboratory care work force," an ACLA spokesperson told ABC News.

COVID-19 infections have increased laboratory staff sick leave -- a "significant factor in determining overall capacity" at an industry-wide level, the spokesperson said.

"We have been pressured to get our capacity where we believe it can be because of the labor problems we see," Quest Diagnostics CEO Steve Rusckowski said Wednesday at the JPM Healthcare Conference. "Some of this is just getting the labor to do our work, but secondly, is because of callouts because of the virus have been considerable over the last two weeks."

-ABC News' Sasha Pezenik