Assistant Secretary of Defense for Public Affairs John Kirby tweeted that the Pentagon is "pausing" the plan to move forward with vaccinations for detainees at Guantanamo Bay.

"We’re pausing the plan to move forward, as we review force protection protocols," Kirby said. "We remain committed to our obligations to keep our troops safe."

No detainees have been vaccinated yet, he said.

ABC News’ Molly Nagle contributed to this report.

Hard-hit California has surpassed 40,000 deaths from COVID-19, according to the state’s Department of Public Health.

At least 40,216 people in the Golden State have lost their lives, which equals about 1 in every 1,000 Californians.

ABC News’ Matt Fuhrman contributed to this report.

Nashville's Music City Center opened Saturday as a mass vaccination site.

Those 75 and older who already have an appointment booked can get vaccinated at the concert venue, according to ABC Nashville affiliate WKRN.

"We think that we’ll be able to do up to 1,000 first doses here and up to 1,000 second doses here a day, once we receive enough vaccine for that,” Metro Nashville Health Department Interim Medical Director Gill Wright told WKRN.

One case of the South African B.1.351 variant has been confirmed in the Baltimore metro region, Maryland Gov. Larry Hogan said.

"The individual has not traveled internationally, making community transmission likely," Hogan’s office said. "Comprehensive contact tracing efforts are underway to ensure that potential contacts are quickly identified, quarantined, and tested.

"The B.1.351 variant has not been shown to cause more severe illness or increased risk of death when compared to other variants. The variant is believed to be more transmissible than other strains," Hogan’s office said. "Additional research is still required to determine the effectiveness of available vaccines against the B.1.351 variant. However, initial evidence suggests that vaccines are still likely to be protective against the variant."

The United States’ first cases of the South African variant were confirmed this week in two people in South Carolina.

The World Health Organization cited new economic research during a press conference Monday, which warns that vaccine nationalism could cost high-income countries $4.5 trillion. Universal vaccination may make it feel as though life is getting back to normal in wealthy countries, but global trade will suffer if poorer nations still have active COVID-19 transmissions, according to research from the International Chamber of Commerce.

"They will not only feel the hit but bear half the cost," said John W.H. Denton AO, secretary general of the ICC. "If you actually want to fix your own economy you're going to have to get involved in fixing the global economy and part of that is that vaccines flow globally and equitably."

Countries need to focus on the tools we already have to drive down COVID-19 transmissions, according to Dr. Bruce Aylward, adviser to WHO Director General Dr. Tedros Adhanom Ghebreyesus.

"If any country bets everything on the vaccine we're going to lose," Aylward said.

-ABC News' Christine Theodorou contributed to this report.