US President Joe Biden tested positive for Covid-19 on Thursday, with his doctors saying the 79-year-old leader was experiencing only mild fatigue and would isolate at the White House while carrying out his duties.
Biden, who posted a picture of himself working at his desk, tweeted that he was "doing great" -- and apologised for missing a scheduled event in Pennsylvania.
He also released a short video clip filmed on a White House balcony, saying: "I really appreciate all your inquiries and concern, but I am doing well... it's going to be OK."
Announcing Biden's diagnosis, the White House stressed that the president was fully vaccinated and twice boosted, and said he was "experiencing very mild symptoms."
It said Biden was taking Pfizer's Paxlovid pill, an antiviral used to minimize the severity of Covid-19.
"Consistent with CDC (Centres for Disease Control and Prevention) guidelines, he will isolate at the White House and will continue to carry out all of his duties fully during that time," it added in a statement.
Fatigue, runny nose and a dry cough
Biden's doctor Kevin O'Connor wrote in an official note that the president was suffering from fatigue, runny nose and a dry cough, starting on Wednesday evening.
O'Connor added that the president had tested positive in a rapid antigen test on Thursday morning before the result was confirmed by a PCR (polymerase chain reaction) test.
"I talked to him just a few minutes ago. He's doing fine, he's feeling good," First Lady Jill Biden, who tested negative, told reporters on a visit to a school in Michigan.
Joe Biden is reported to be in good general health, but his advanced 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, as well as declining personal approval ratings.
His ratings have hit a new low, with only 31 percent of Americans satisfied with the way he is running the country, according to the latest polls.
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.
He is now expected to stay at the White House for several days.
The CDC, the leading US government health agency, says that older adults are more likely to get severely sick from Covid-19, with risk increasing with age.
The highly-transmissible Omicron BA.5 sub-variant is currently fuelling a new wave of Covid cases in the United States -- where hospitalisations have doubled in recent months.
The country is seeing some 130,000 new reported cases daily, but the figure is thought to be substantially underestimated due to the expanded use of home tests, whose results are not typically reported to authorities.
On assuming office, Biden made a point of abiding by strict Covid protocols, holding socially distanced meetings or Zoom gatherings, and wearing a mask to public events — in sharp contrast to his predecessor Donald Trump.
Remained Covid free
While other members of the Biden's family and many of his close advisors contracted the virus, the president had remained Covid free until Thursday.
Trump tested positive for coronavirus in October, 2020 -- in the middle of the bitterly fought election race he eventually lost to Biden.
The news that he and the first lady, Melania Trump, had both contracted Covid 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 Centre, where he spent the weekend and received various treatments. He returned to the White House three days later.
Biden last tested negative on Tuesday, and his officials pledged to provide a daily update on his health "out of an abundance of transparency."
Kamala Harris negative
After Biden's positive result, the White House said that Vice President Kamala Harris, who caught Covid back in April, had tested negative.
Good wishes poured in from US politicians across the country's sharp divide as well as from abroad.
"Wishing you... a swift recovery from #Covid19. Stay strong!" tweeted World Health Organization chief Tedros Ghebreyesus.
"Wishing President Biden a speedy recovery from Covid," said leading US Republican Lindsey Graham.