Secretary of State Mike Pompeo is in quarantine after being exposed to someone who tested positive for coronavirus, according to a State Department spokesperson.

It’s unclear when or where the top U.S. diplomat was exposed or by whom, a detail the State Department said it won’t confirm for privacy reasons. But he has tested negative and remains under monitoring by the department’s medical team, the spokesperson said.

Pompeo was scheduled to deliver remarks at a holiday reception for U.S. diplomats in dangerous posts and their families Tuesday, but did not show up, according to two State Department sources.

Despite warnings by the Centers for Disease Control and Prevention against large gatherings, the agency has gone ahead with holiday parties, garnering a public backlash, especially from its critics on Capitol Hill.

The State Department has not yet responded to further questions. Pompeo was expected to attend a Cabinet meeting with President Donald Trump at the White House Wednesday as well as another holiday reception this evening, but his public schedule now says he has no public appointments.

It’s unclear if that reception, for foreign ambassadors and chiefs of mission posted in Washington and their spouses, will happen without him.

The event Tuesday for “Unaccompanied Tour Families” was attended by a couple dozen guests, according to the one of the sources, mostly families of diplomats serving in countries like Afghanistan, Iraq, Somalia, and Pakistan where spouses or children are not allowed to join them.

Hundreds of guests were invited, prompting outrage given the public health warnings about indoor gatherings. AFSA – the American Foreign Service Association, the Foreign Service union, called on Pompeo to cancel it. But far fewer were expected to attend, as in years past, because many families don’t live in the Washington, D.C., area and would have to travel.

Last week, the department held another reception for foreign diplomats and other VIP guests at Blair House, the president’s historic guesthouse where visiting heads of state often stay. That reception was hosted by acting chief of protocol Cam Henderson, not Pompeo.

Guests at the various formal receptions were not tested before arriving, but they were given temperature checks and required to social distance and wear masks, except when eating or drinking, a State Department spokesperson told ABC News earlier this month.

On Thursday, Pompeo was also reportedly going to meet Tony Blinken, President-elect Joe Biden’s choice to succeed him as secretary. A State Department spokesperson told ABC News there was “no meeting planned or confirmed,” although Pompeo had said this week he planned to meet Blinken “at the right time.” It’s unclear if a meeting will be postponed or take place via video teleconference.

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 Tuesday.

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 Afghanistan, Iraq, and Somalia, 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 or whether Pompeo would receive one.

But he identified five groups of employees who will begin receiving them right away: 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.”

Pompeo and his staff likely fall under Bulatao’s “critical operations” category, especially since his diplomatic security detail appears to make the list. Acting Defense Secretary Chris Miller was vaccinated on Monday, the only cabinet secretary known 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 Tuesday 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.”