By Kanishka Singh WASHINGTON (Reuters) -U.S. President Joe Biden is feeling well and continuing his isolation measures after again testing positive for COVID-19, his physician said in a memo released by the White House on Sunday. Biden tested positive for COVID again on Saturday in what the White House doctor described as a “rebound” case seen in a small percentage of patients who take the antiviral drug Paxlovid. “Given his rebound positivity which we reported yesterday, we continued daily monitoring. This morning, unsurprisingly, his SARS-CoV-2 antigen testing remained positive,” the physici…