The causative agent for U.S. President Joe Biden's COVID-19 infection is "most likely" the Omicron BA.5 variant, his physician said on Saturday.

Biden's symptoms, sore throat, runny nose, loose cough, and body aches, continue to improve, Dr. Kevin O'Connor announced in a memo to the White House after preliminary sequencing results had returned.

"His voice remains deep," O'Connor added. "His pulse, blood pressure, respiratory rate and temperature remain entirely normal. His oxygen saturation continues to be excellent on room air. His lungs remain clear."

Biden, 79, is tolerating treatment well and will continue to take Paxlovid, an antiviral pill treatment produced by Pfizer and given to patients with COVID-19, according to O'Connor.

The White House announced on Thursday morning that Biden had caught the coronavirus. He is now quarantining at the White House and continues to carry out his duties.

Biden has been participating in "virtual conference call meetings," the White House chief of staff Ron Klain said, adding "he's been on the phone," according to CNN. 

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases told CNN the President "is in a position to be able to test every day and wait till he becomes negative before he goes back."

BA.5, an Omicron subvariant and the most transmissible COVID-19 mutant to date, is responsible for at least 75 percent of new infections across the U.S.

The total number of COVID-19 cases in the U.S. has exceeded 90 million, with over one million related deaths, according to the latest data from Johns Hopkins University.