Washington, July 24 : The causative agent for US President Joe Biden's Covid-19 infection is "most likely" the Omicron BA.5 variant, his physician has said. 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 on Saturday. "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, Xinhua news agency quoted O'Connor as saying. The White House announced on Thursday morning that Biden had been infected with the virus. 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 US lawmakers who had contracted the disease in recent months. BA.5, an Omicron sub-variant and the most transmissible Covid-19 mutant to date, is responsible for at least 75 per cent of new infections across the US. The total number of Covid-19 cases in the US has exceeded 90 million, with over 1 million deaths, according to the latest data from Johns Hopkins University. /IANS