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.

Russia said Friday it will be ready to supply Europe with enough doses of its COVID-19 vaccine, Sputnik V, for 50 million people in the second quarter of this year.

The Russian Direct Investment Fund (RDIF), which is responsible for worldwide marketing of the vaccine, announced via Twitter that 100 million doses can be provided to the European Union -- pending regulatory approval -- once most of Russia's population has been vaccinated.

After being developed by the state-run Gamaleya Research Institute of Epidemiology and Microbiology in Moscow, Sputnik V was controversially registered by the health ministry in August before starting crucial Phase 3 trials, with Russia declaring itself the first in the world to register a COVID-19 vaccine.

The RDIF said the vaccine is now registered in 15 countries and that documents have been submitted to the European Medicines Agency (EMA) for "rolling review," which would mean that the drug regulator is reviewing clinical trial data on a rolling basis. However, last week, the EMA said in a statement that "currently Sputnik V is not undergoing a rolling review."

ABC News' Alina Lobzina contributed to this report.