President Joe Biden's COVID-19 symptoms continue to improve and now include "less troublesome" sore throat, runny nose, loose cough and body aches, his physician, Dr. Kevin O'Connor, said in a memo on Saturday.

Biden's lungs remain clear and his oxygen saturation "continues to be excellent on room air," the doctor said.

Biden, 79, tested positive for COVID on Thursday, when the White House said he was experiencing mild symptoms. His diagnosis came as a highly contagious subvariant of the coronavirus drives a new wave of cases in the United States.

Biden most likely has that BA5 variant, O'Connor said.

"The President continues to tolerate treatment well. We will continue PAXLOVID as planned," he said, referring to the Pfizer Inc antiviral drug the president is taking.

Biden is not experiencing shortness of breath, O'Connor said. "The BA5 variant is particularly transmissible and he will continue to isolate," O'Connor said. "We will continue to monitor him closely, during this very common outpatient treatment regimen."

The White House has sought to underscore Biden's ability to work through his illness. On Thursday it released a video of the president reassuring Americans he was doing fine, and on Friday he participated in virtual meetings with White House staff.

His schedule showed no presidential events over the weekend. The president's wife, first lady Jill Biden, is at their home in Wilmington, Delaware. She tested negative for COVID-19 on Saturday morning, according to her spokesperson, Michael LaRosa.

The White House has not said where Biden contracted the virus. He recently returned from a trip to the Middle East and held public events before that trip in which he had close personal interactions with scores of people.

Biden's diagnosis is the latest challenge he has faced amid threats to his policy agenda on Capitol Hill and high inflation putting his fellow Democrats at risk of losing control of Congress in the November midterm elections.