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.

There were 152,478 new cases of COVID-19 confirmed in the United States on Wednesday, according to a real-time count kept by Johns Hopkins University.

Wednesday's case count is far less than the country's all-time high of 300,282 newly confirmed infections on Jan. 2, Johns Hopkins data shows.

An additional 3,943 fatalities from COVID-19 were registered nationwide on Wednesday, down from a peak of 4,466 new deaths on Jan. 12, according to Johns Hopkins data.

COVID-19 data may be skewed due to possible lags in reporting over the Martin Luther King Jr. Day holiday weekend.

A total of 25,598,062 people in the U.S. have been diagnosed with COVID-19 since the pandemic began, and at least 429,195 have died, according to Johns Hopkins data. The cases include people from all 50 U.S. states, Washington, D.C., and other U.S. territories as well as repatriated citizens.

Much of the country was under lockdown by the end of March as the first wave of pandemic hit. By May 20, all U.S. states had begun lifting stay-at-home orders and other restrictions put in place to curb the spread of the novel coronavirus. The day-to-day increase in the country's cases then hovered around 20,000 for a couple of weeks before shooting back up over the summer.

The numbers lingered around 40,000 to 50,000 from mid-August through early October before surging again to record levels, crossing 100,000 for the first time on Nov. 4, then reaching 200,000 on Nov. 27 before topping 300,000 on Jan. 2.

So far, the U.S. Food and Drug Administration has authorized two COVID-19 vaccines for emergency use -- one developed by U.S. pharmaceutical giant Pfizer and its German partner BioNTech, and another developed by American biotechnology company Moderna and the National Institute of Allergy and Infectious Diseases. More than 24 million vaccine doses have been administered nationwide, according to the latest data from the Centers for Disease Control and Prevention.