The State Department is receiving its first COVID-19 vaccines this week, according to an internal email from a senior official obtained by ABC News.

The “very limited number” of vaccines the department will receive will go to a small group of employees deemed mission critical or most at-risk, including front-line medical personnel and those serving in three countries with poor health care systems, Under Secretary of State for Management Brian Bulatao said in his email.

“While we would have preferred to vaccinate our entire Department workforce at once, we will have to do so incrementally based on vaccine availability,” Bulatao said, noting the agency is working with the Pentagon’s Operation Warp Speed and the Department of Health and Human Services on this.

Bulatao did not say how many vaccines the agency will get but identified five groups of employees who will begin receiving them: Front-line medical personnel, including the doctors and nurses serving in Washington, D.C., and at embassies overseas; employees at the agency’s 24/7 watch center; those working on “critical operations, maintenance, and custodial staff”; “mission-critical” diplomatic security staff in DC; and American personnel serving in Iraq, Afghanistan and Somalia, where “local conditions... can exacerbate the disease burden and the challenges of providing medical support services in these locations.”

It’s unclear whether that includes Secretary of State Mike Pompeo himself and his staff, although they likely fall under Bulatao’s “critical operations” category and his diplomatic security detail appear to make the list. Acting Defense Secretary Chris Miller was vaccinated on Monday, the only cabinet secretary to get one so far.

A State Department spokesperson declined to offer details of the agency’s plans, citing “operational sensitivity,” but added in a statement to ABC News that any vaccines obtained through Operation Warp Speed will “allow the Department to advance U.S. national security interests and ensure America’s essential diplomacy continues unimpeded.”

-ABC News' Conor Finnegan

Biden is expected to name former 2020 rival and South Bend Mayor, Pete Buttigieg to head the Department of Transportation, sources familiar with the transition tell ABC News.

If confirmed Buttigieg, 38 would be the youngest pick yet for Biden's cabinet, and the first openly gay cabinet secretary approved by the U.S. Senate to serve in U.S. history.

Buttigieg endorsed Biden in March shortly after ending his own presidential campaign and campaigned on behalf of Biden during the general election. Biden, spoke highly of Buttigieg following his endorsement, saying he reminded Biden on his late son, Beau.

-ABC News' Molly Nagle, Justin Gomez and Katherine Faulders

Speaking on the tarmac in Delaware ahead of his trip to Georgia to campaign for Democratic candidates in the Senate runoffs there, Biden confirmed he spoke with Senate Majority leader Mitch McConnell -- who acknowledged Biden's victory for the first time on Tuesday -- saying they had a "good conversation" and expressed his hope that they could work together in the future.

"I had a good conversation with Mitch McConnell today. We talked -- so I called to thank him for the congratulations, told him although we disagree on a lot of things, there’s things we can work together on. We’ve always been straight with one another, and we agreed we’d get together sooner than later. And I’m looking forward to working with him," Biden said.

Biden went on to tell reporters that he has been speaking with other members of Congress, saying about “a dozen” have been calling him. Biden promised to tell the press who he has spoken to.

“I just want you to know I spoke with him, and I’ve been calling other members. I spoke with some other members as well," Biden said. "As I tick them off I’ll tell you who’s calling."

Asked when he would receive the coronavirus vaccine, which Biden has said he'll do publicly, he confirmed that it would be soon but stressed that he wanted to do it “by the numbers."

“Dr. Fauci recommends I get the vaccine sooner than later.I want to just make sure we do it by the numbers, and we do it -- but when I do it, you’ll have notice and we’ll do it publicly,” Biden said.

-ABC News' Sarah Kolinovsky, John Verhovek and Molly Nagle

The top State Department official for conflict operations is resigning, according to internal emails obtained by ABC News.

Denise Natali, the assistant secretary of state for conflict and stabilization operations, will depart the agency Friday, telling her staff in an email Tuesday, "It has been an honor to work with you for the past two years. I am extremely grateful for your commitment, hard work, and support."

"You are making significant contributions to U.S. foreign policy, particularly in carrying out our mission to anticipate, prevent, and respond to conflict that undermines U.S. national interests. I am very proud of what you have accomplished and am confident that you will continue to do great work in the years ahead," she added.

Natali is the first senior department official appointed by Trump and confirmed by the Senate to resign after Biden defeated their boss in the 2020 presidential election. Jim Jeffrey, a veteran diplomat who was Secretary of State Mike Pompeo's special envoy for Syria, departed in November.

A State Department spokesperson confirmed to ABC News her last day is Friday.

Natali joined the Trump administration in October 2018 from the National Defense University. During her tenure, she led U.S. delegations from Colombia to Niger to Bulgaria on countering violent extremism, coordinating responses with U.S. allies, reintegrating terrorist fighters and stabilizing conflict-ridden countries.

Her note made no mention of the 2020 election. But the department has been working with Biden's transition team, providing briefings and office space, even as Pompeo has yet to fully acknowledge Biden's victory. The agency "will do everything that's required by law" to facilitate the transition, he said on Nov. 24, two weeks after quipping there would be a "smooth transition to a second Trump administration."

CNN reported Tuesday that includes a meeting this Thursday between him and Biden's choice to succeed him, Anthony Blinken, which would be their first. A State Department spokesperson told ABC News, "There is no meeting planned or confirmed," after Pompeo told the Washington Examiner Monday they'll meet "at the right time."

-ABC News' Conor Finnegan