WASHINGTON, July 23 (Xinhua) -- The causative agent for U.S. President Joe Biden's COVID-19 infection is "most likely" the BA.5 variant, his physician said on Saturday.

Biden's symptoms continue to improve, with sore throat, runny nose, loose cough, and body aches, 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 therapy 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 joined a long list of officials in his administration and U.S. lawmakers who had tested positive for COVID-19.

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 United States.

The total number of COVID-19 cases in the United States has exceeded 90 million, with over 1 million related deaths, according to the latest data from Johns Hopkins University.