Joe Biden, the oldest person ever to serve as president of the United States, 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 a runny nose, fatigue and an occasional dry cough, which he began to experience late on Wednesday, White House physician Kevin O’Connor said in a note made public on Thursday. Biden has begun taking the antiviral treatment Paxlovid, O’Connor said.

“He is fully vaccinated and twice boosted and experiencing very mild symptoms,” press secretary Karine Jean-Pierre 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.

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

Biden’s administration is facing major challenges including soaring inflation and Russia’s land assault on Ukraine. His popularity has dropped sharply over the past year. A Reuters/Ipsos survey completed on Tuesday showed 36percent of Americans approve of his job performance.

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.

Covid on the rebound

While many Americans have moved on from the strict precautions of the pandemic's early months, returning to offices and schools and resuming summer travel, the virus continues to spread.

Cases in the United States are up more than 25percent in the last month, according to CDC data, as the rapidly spreading BA.5 subvariant has taken hold.

Evading the immune protection afforded either by vaccination or prior infection, BA.5 has been the dominant subvariant in the United States since at least early July and has driven a surge of new infections globally.

Biden is tested regularly for the disease and anyone who meets with him or travels with him is tested beforehand, the White House has said. Biden had last tested negative on Tuesday.

If given within the first five days of infection, the Pfizer Inc antiviral drug Paxlovid that Biden is taking has been shown to reduce the risk of severe disease by nearly 90 percent in high risk patients.

But Paxlovid has in some cases been associated with rebound infections, in which patients improve quickly and test negative after a five-day course of the drug, but then days later symptoms return.

Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, experienced a rebound infection four days after ending his first course of Paxlovid, and was given a second round of the drug, Fauci said in an interview this week.

Biden’s White House predecessor, Donald Trump, contracted Covid-19 and was hospitalized for three nights in October 2020.

Biden is fully vaccinated and got his second booster shot in March. The risk of an unvaccinated person aged 65 and older being hospitalized after contracting Covid-19 is 10 times that of someone who has been vaccinated.

Unlike Trump, Biden consistently wore a mask when in public when case counts were high and before being vaccinated.

He also set up strict Covid-19 safety protocols at the White House, urged Americans to take the virus seriously and campaigned for everyone to get fully vaccinated.

Biden has, however, stopped wearing a mask at public events in recent months, and the White House dropped its mask requirement ahead of his March 1 State of the Union Address.

Biden joins a roster of other world leaders who have contracted Covid since the pandemic started in early 2020.

Those include British Prime Minister Boris Johnson, French President Emmanuel Macron, President Jair Bolsonaro of Brazil, Canadian Prime Minister Justin Trudeau and Albert II, the prince of Monaco. All have recovered.

Trump was Hospitalized

A month before he lost the 2020 presidential election to Biden, Trump was hard-hit by the virus. He, his wife Melania and other White House staff contracted it after the administration held an event for new Supreme Court Justice Amy Coney Barrett in September 2020.

Trump, then 74, was hospitalized on Oct. 2, 2020, and underwent aggressive treatment at Walter Reed National Military Medical Center in a suburb of Washington. His low oxygen levels alarmed his medical team.

The former president’s previous physical showed he was in the obese category, which made him more likely to require hospitalization.

“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!”

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.

Administration officials have acknowledged that Biden’s regular contact with advisers and supporters could expose him to Covid-19.

However, the administration is keen to project a sense of normalcy as many Americans are returning to work and socializing with friends and family, officials have said. On Wednesday he traveled to Rhode Island and Massachusetts for a speech on climate change.

“We all knew this would happen, it was just a matter of time. Given the hectic schedule of the POTUS and the super high transmissibility of BA.5,” Dr. Peter Hotez, a virologist and dean of Baylor College of Medicine’s National School of Tropical Medicine, tweeted.

Biden's wife Jill tested negative on Thursday morning in Detroit and plans to maintain her full schedule of travel in Michigan and Georgia, according to her spokesman Michael LaRosa.

Asked by Reuters on Wednesday what the country should do with Covid cases on the rise, Biden encouraged vaccination.

“It’s not in their interest or the public’s interest not to get vaccinated,” Biden, told reporters at Joint Base Andrews, referring to people who were not vaccinated. “We have the capacity to control it. They should get vaccinated now.”