By Jarrett Renshaw and Pete Schroeder WASHINGTON (Reuters) -U.S. President Joe Biden tested positive for COVID-19 again on Saturday morning in what the White House doctor describes as a “rebound” case seen in a small percentage of patients who take the antiviral drug Paxlovid. Biden, 79, who emerged from COVID isolation on Wednesday after testing positive on July 21, will now return to strict isolation and will cancel planned trips to his home in Wilmington and work trip in Michigan, the White House said. Biden held public events on Wednesday and Thursday, but none on Friday. Biden had planned…