President Joe Biden tested positive for Covid-19 on Thursday, his administration announced, saying the 79-year-old leader was experiencing "mild symptoms" and would carry out his full duties while isolating at the White House.
Biden had been due to travel to Pennsylvania during the day, the latest in a series of trips around the country as he seeks to revive waning Democrat fortunes ahead of midterm elections.
"He is fully vaccinated and twice boosted and experiencing very mild symptoms," the White House said in a statement, adding that Biden had begun taking Pfizer's anti-Covid pill Paxlovid.
"Consistent with CDC guidelines, he will isolate at the White House and will continue to carry out all of his duties fully during that time."
Biden is reported to be in good general health, but his age will heighten concern over the impact of Covid.
Politically he is in a tough phrase of his presidency, facing November midterm elections that are forecast to be painful for his Democratic Party, and declining personal approval ratings.
According to a study conducted by Quinnipiac University in the state of Connecticut and released Wednesday, Biden's approval ratings have hit a new low, with only 31 percent of Americans satisfied with the way he is running the country.
Biden had planned to spend more time on the ground in the United States in the coming weeks after a period of intense overseas travel, including a NATO summit in Spain and a controversial trip to Saudi Arabia.
Biden's predecessor Donald Trump had tested positive for coronavirus in October, 2020 -- in the middle of their bitterly fought election race.
The news that he and the first lady, Melania Trump, had both contracted the virus was a shocking development at a time when the pandemic was still unfolding across the globe.
Trump, who was 74 at the time, was transferred to Walter Reed National Military Medical Center, where he spent the weekend and received various treatments. He returned to the White House three days later.
The White House said Biden had last tested negative on Tuesday.
"Out of an abundance of transparency, the White House will provide a daily update on the president's status as he continues to carry out the full duties of the office while in isolation," it said.
"Per standard protocol for any positive case at the White House, the White House Medical Unit will inform all close contacts of the president during the day today, including any members of Congress and any members of the press who interacted with the president during yesterday’s travel."