By Kanishka Singh and Jeff Mason WASHINGTON (Reuters) -U.S. President Joe Biden’s condition since contracting COVID-19 has improved considerably and his greatest symptom now is a sore throat, his physician said on Sunday. Biden’s cough and body aches have diminished since he tested positive for the coronavirus on Thursday and he is not experiencing any shortness of breath, the physician, Dr. Kevin O’Connor, said in a memo released by the White House. “His symptoms continue to improve significantly. His predominant symptom now is sore throat. This is most likely a result of lymphoid activation …