Pentagon chief Lloyd Austin has tested positive for COVID-19, according to a statement from him released by the Pentagon.
Austin is fully vaccinated and received a booster in early October. He last met President Joe Biden on Dec. 21, over a week before he began experiencing symptoms.
"As my doctor made clear to me, my fully vaccinated status — and the booster I received in early October — have rendered the infection much more mild than it would otherwise have been," Austin added.
Austin said he had requested a test earlier on Sunday after having symptoms while at home on vacation.
He was last at the Pentagon on Thursday. "I met briefly - and only - with a few members of my staff. We were properly masked and socially distanced throughout."
Last week, the US Centers for Disease Control and Prevention shortened the recommended times that people should isolate if they have tested positive from 10 days to five days provided that they do not have symptoms and wear a mask around others for at least five more days.
Austin said he will remain at home for the next five days "in accordance with CDC guidelines."
"To the degree possible, I plan to attend virtually this coming week those key meetings and discussions required to inform my situational awareness and decision making. I will retain all authorities," Austin said.
This comes after the Defense Department last week tightened restrictions at its headquarters over concern about the highly transmissible Omicron variant.
The military is confronted with the challenge of maintaining military preparedness for troops, often in close quarters on ships and planes.
In August, the Pentagon mandated that US military service members get fully vaccinated against COVID-19. However, a small number of Republican governors have pushed back against the mandate for National Guard members in their states.
Oklahoma's Republican governor, for instance, has requested that the military's vaccine mandate be halted. However, a federal judge last week denied the request, saying the state’s National Guard members must get vaccinated.
Austin is one of the most senior members of the Biden's administration to test positive for COVID-19.
In October, Homeland Security Secretary Alejandro Mayorkas tested positive for the virus.
On Saturday, at least 346,869 new coronavirus were recorded in the US, according to a Reuters tally. The country’s death toll rose by at least 377 to 828,562.
As of Dec. 25, the Omicron variant was estimated to be 58.6% of the coronavirus variants circulating in the United States, according to data from the US Centers for Disease Control and Prevention (CDC).