Joe Biden, the oldest person ever to serve as U.S. president, has tested positive for Covid-19, is experiencing mild symptoms and will continue working but in isolation, the White House said on Thursday.

Biden, 79, has begun taking a course of the antiviral treatment Paxlovid, according to his press secretary, Karine Jean-Pierre.

"He is fully vaccinated and twice boosted and experiencing very mild symptoms," she said in a statement.

"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," she said, referring to the Centers for Disease Control and Prevention.

Multiple members of Biden's administration and other senior figures in Washington have tested positive for the coronavirus in recent months, including Vice President Kamala Harris in April, House of Representatives Speaker Nancy Pelosi and Attorney General Merrick Garland.

All have since tested negative and resumed working.

Jean-Pierre said Biden had been speaking with his staff by phone and will continue taking part in meetings by phone and Zoom from the White House while he recovers. He will resume in-person work once he tests negative, she said.

The White House will provide a daily update on the president's health, Jean-Pierre said.

CNN, citing White House Covid coordinator Ashish Jha, said Biden has a runny nose and fatigue but no fever

Biden's Republican predecessor, Donald Trump, contracted Covid-19 in late 2020 and was hospitalized for several days.

"We are in a very different place than the last time a POTUS got Covid," Ezekiel "Zeke" Emanuel, a physician and former member of Biden's Covid transition team, wrote on Twitter.

"Biden is fully vaxxed/boosted and reportedly on a therapeutic (Paxlovid) that significantly mitigates symptoms. If anything, this shows how contagious BA5 is. Feel better, @POTUS!"