Dr. Anthony Fauci, the nation’s leading infectious disease expert, has tested positive for COVID-19 for the first time.

The National Institutes of Health announced the diagnosis Wednesday, confirming the 81-year-old is now in isolation and experiencing “mild symptoms.” Fauci—the longtime director of the NIH’s National Institute of Allergy and Infectious Diseases—is reportedly fully vaccinated and has been boosted twice.

Dr. Fauci was set to appear before Senate Health, Education, Labor and Pensions Committee on Thursday to provide an update on the government’s response to the pandemic. It’s unclear if his appearance has been rescheduled, or if he’ll address the committee virtually. The NIH said Fauci will work from home during his isolation.

“Dr. Fauci will follow the COVID-19 guidelines of the Centers for Disease Control and Prevention and medical advice from his physician and return to the NIH when he tests negative,” the agency’s statement read. 

The NIH said Fauci has not recently been in close contact with any senior government official, including President Joe Biden. Fauci is POTUS’ chief medical adviser, a position he’s held since it was established under the Trump administration in 2019. He previously said he would resign from the post if Trump were re-elected in 2024; however, in a recent interview with Fox News’ Neil Cavuto, Fauci clarified he will likely step down regardless of who is in office.

“Well, I’m not going to get involved in any politics about who is or is not going in the White House,” he said. “By the way, by the time that happens, I think I won’t be around, no matter who the president is.

Cavuto then asked Fauci if he believed his job was “done.”

“No, I’m not done yet,” the doctor responded. “But you’re talking about a few years from now. And I don’t foresee that I will be doing this a few years from now.”