United States President Joe Biden has tested positive for COVID-19 again on July 30, days after testing negative for the virus.

"After testing negative on Tuesday evening, Wednesday morning, Thursday morning and Friday morning, the President tested positive late Saturday morning, by antigen testing," the White House said.

Biden’s physician Kevin O'Connor noted that it represents 'rebound' positivity, which is observed in a small percentage of patients treated with PAXLOVID. He added there is no need to initiate treatment as Biden has experienced no reemergence of symptoms and continues to feel quite well.

"As described last week, acknowledging the potential for so-called "rebound" COVID positivity observed in a small percentage of patients treated with PAXLOVID, the President increased his testing cadence, both to protect people around him and to assure early detection of any return of viral replication," White House Physician said.

"This in fact represents ‘rebound’ positivity. The President has experienced no reemergence of symptoms and continues to feel quite well. This being the case, there is no reason to reinitiate treatment at this time, but we will obviously continue close observation," he added.

Meanwhile, the White House said that the US President will continue to follow the strict isolation procedures.

"However, given his positive antigen test, he will reinitiate strict isolation procedures. As I've stated previously, the President continues to be very specifically conscientious to protect any of the Executive Residence, White House, Secret Service and other staff whose duties require any (albeit socially distanced) proximity to him," the physician said.