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.

At Friday’s White House press briefing, Dr. Anthony Fauci said the United Kingdom variant will likely become more “dominant” in the U.S. toward the end of March or early April.

There are 379 confirmed cases across 29 states of the B117 strain of the coronavirus, according to CDC director Dr. Rochelle Walensky.

Fauci indicated that the evolving nature of the virus is something the medical community will have to continue dealing with going forward.

“Even though the long-range effect in the sense of severe disease is still handled reasonably well by the vaccines, this is a wake-up call to all of us, that we will be dealing, as the virus uses its devices to evade pressure, particularly immunological pressure, that we will continue to see the evolution of mutants,” he said.

Fauci also indicated that the fight to contain the new variants will impact the vaccine response.

“We, as a government, the companies, all of us that are in this together, will have to be nimble to be able to just adjust readily to make versions of the vaccine that actually are specifically directed towards whatever mutation is actually prevalent at any given time,” he said.

ABC News’ Matthew Vann contributed to this report.