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.

British Prime Minister Boris Johnson has indicated that England's lockdown restrictions will remain in place until at least early March.

In a statement to lawmakers at the U.K. House of Commons on Wednesday, Johnson said officials "do not yet have enough data to know exactly how soon it will be safe to reopen our society and economy." But he expressed hope that schools could reopen from March 8, so long as his government meets its target of vaccinating everyone in the top four priority groups by mid-February.

The prime minister also announced new restrictions for travelers arriving in England from countries deemed to be high-risk. He said the United Kingdom remains in a "perilous situation" with more than 37,000 people hospitalized with COVID-19 -- almost double the amount during the previous peak in April.

During a press conference later Wednesday, Johnson told reporters that March 8 was the "earliest" date by which the government could "responsibly" allow schoolchildren to return to classrooms.

The comments come after the U.K. became the fifth country in the world to record more than 100,000 deaths from COVID-19.

England entered its third national lockdown of the coronavirus pandemic on Jan. 5.

Although Johnson is the prime minister of the U.K., his administration is only responsible for COVID-19 restrictions in England because public health legislation is devolved to national governments within the U.K., meaning that Scotland, Wales and Northern Ireland are responsible for their own coronavirus-related policies.