Los Angeles' Dodger Stadium will open as one of the largest mass vaccination sites in the country on Friday, officials announced.

The stadium will have the capacity to vaccinate 12,000 people a day, LA Mayor Eric Garcetti said during his COVID-19 briefing Thursday.

Eligibility in Los Angeles County currently is limited to health care workers and seniors in nursing facilities.

The vaccination push comes as 1 in 3 people in LA County has been infected with COVID-19, Garcetti said. The county reported 17,323 new cases on Thursday.

"Our numbers remain very high. We remain one of the epicenters of this disease across the country," Garcetti said, though he added that there are signs that hospitalizations may be stabilizing.

ABC News' Cammeron Parrish contributed to this report.

Weeks after video emerged of mostly maskless partygoers at U.S. President Donald Trump's Mar-a-Lago Club in Palm Beach, county officials are cracking down.

Palm Beach County sent a letter this week, acquired by ABC News, warning the club and saying officials had met with representatives from the club about violations. Masks are mandatory in the county in all businesses or establishments, and anywhere in public social distancing cannot be maintained. The mandate is currently in place through Jan. 20 -- the same day the county's most famous resident will be exiting the White House.

"Thank you for meeting with us last week to discuss the concerning allegations regarding the Mar a Lago New Year's Eve party and lack of facial coverings being worn during evening activities," the county wrote in the letter addressed to Bernd Lembcke, executive vice president and managing director of Mar-a-Lago Club.

"We recount that you provided masks for all party goers who attended the party and that you provided additional masks for those that walked from the reception area to the main dining ballroom," the letter continued. "Although you provided these important steps, it seemed that based on the video evidence, there was a breakdown in enforcement of the mask orders that led to almost the entire room of guests being without masks during the later evening activities."

The letter also includes a confirmation of the violation, which is a first-time warning, that lays out a fine of up to $15,000 for each potential future violation.

Trump has consistently downplayed wearing masks over the course of the entire pandemic. Despite telling people to wear masks on occasion at official briefings, he also mocked others for wearing them, including President-elect Joe Biden. Many supporters have decried mandates and openly flouted rules, including maskless Trump supporters who stormed the Capitol last week.

ABC News' Will Gretsky contributed to this report.

The U.S. death toll from COVID-19 continues to climb in the weeks following the end-of-year holidays. Fatalities from the disease nationwide are currently 25% higher than at any other time during the coronavirus pandemic, according to The COVID Tracking Project, a volunteer-run effort to track the U.S. outbreak.

"For scale, COVID-19 deaths reported this week exceed the CDC's estimate of 22K flu-related deaths during the entire 2019-2020 season," The COVID Tracking Project wrote on Twitter Thursday.

There were 3,915 deaths from COVID-19 registered nationwide on Thursday, well above a seven-day average that continues to rise. However, COVID-19 cases and hospitalizations were under the seven-day average on Thursday.

The one bit of good news highlighted by The COVID Tracking Project was that hospitalizations are leveling off. Still, there are 128,947 people currently hospitalized with COVID-19 in the United States, much more than at any other time during the pandemic.

The COVID Tracking Project singled out Alabama, Arizona, California and Florida as particularly concerning locations right now. Arizona currently has the worst per-capita case numbers in the world, according to the project.

A newly identified variant of the virus that causes COVID-19 may have emerged in the U.S. in May and could be one of the predominant versions circulating now, researchers at Southern Illinois University found.

Just because a new variant has emerged doesn't mean it's inherently dangerous, experts cautioned. It’s unknown if this new U.S. variant is more transmissible and deadly, but scientists say they are monitoring and continuing to study newly emerging viral variants. On Wednesday, researchers at Ohio State reported two newly identified ones. On Thursday, researchers at Southern Illinois University said they also identified a new variant, which is likely the same as the two identified in Ohio.

Now, researchers at Southern Illinois University are sharing even more details about this U.S. variant, which they are calling 20C-US. Origins of this variant can be traced to May 2020 from a sample in Texas, they said.

The 20C-US variant appears to be widespread in the Upper Midwest and comprises roughly 50% of the samples in the U.S., said Keith T. Gagnon, coauthor of the study and associate professor at Southern Illinois University.

"Let’s not get overly excited -- but be diligent," Gagon said. "Here it was, underneath our noses, for months."

“It doesn't look like it’s going to get in the way of vaccines," Gagnon added. 

ABC News’ Sean Llewellyn, Eric Strauss and Sony Salzman contributed to this report.