The US president had ended his self-isolation on Wednesday after what the… White House described as a “mild” case of Covid.
However, on Saturday, Mr Biden announced that he would return to self-isolation after testing positive again, but said he had no symptoms and would continue to work.
The 79-year-old said: “Folks, today I tested positive for COVID again. This happens to a small minority of people.
“I have no symptoms, but I am going to isolate for the safety of everyone around me.
“I’m still at work and will be back on the road soon.”
White House doctor Dr. Kevin O’Connor said the president tested negative on Tuesday evening, Wednesday morning, Thursday morning and Friday morning before testing positive on Saturday morning.
He said the infection appeared to be a mild but rare ‘rebound’ case after treatment with an antiviral drug.
Mr Biden had addressed the nation on Wednesday after he appeared to come out of his battle with the condition and end isolation, saying he was “feeling good”.
He said his condition had been mild from a combination of vaccines and the Paxlovid treatment.
He said, “I got through it without fear. A very minor inconvenience due to these essential life-saving aids.
“And guess what, I want to remind everyone: they are free. They’re convenient, they’re safe, and they work.”
dr. O’Connor had previously warned that there was a chance of a rebound infection because Mr Biden had taken Paxlovid.
He said a small percentage of patients treated with Paxlovid had experienced a rebound of their infection after treatment.
Despite this, Paxlovid has been proven to significantly reduce serious illness and death among those most vulnerable to Covid.