The National Institute of Allergy and Infectious Disease, for which Fauci serves as top dog, made the announcement Wednesday, saying Doc had tested positive during a rapid antigen test ... and as a result, was sent home to recover. He'll be back to work when he's negative.

The NIH agency notes he's experiencing mild symptoms, and attributes that to the fact he's fully vaccinated and has also received two booster shots.

Also of note ... Fauci has not been in close contact with President Biden of late, so says NIAID, or any other top government official for that matter. So it seems JB and co. are in the clear on his end -- good news, especially since they've already had close calls.

Several people in Biden's cabinet have caught the virus in recent months -- including former Press Secretary Jen Psaki, and even Vice President Kamala Harris ... ditto for her hubby. Of course, there've been some high-profile Congress members who've gotten sick too.