COVID-19 patients drop rapidly during the weeks after their bodies have cleared the novel coronavirus, and symptoms have subsided, according to a study.In the absence of approved, effective treatments for COVID-19, some hospitals have been treating patients with severe symptoms with blood plasma from recovering patients.If convalescent plasma is ultimately shown to have a clear benefit, the new study published in the journal mBio concluded that it needs to be collected during a specific window of time after recovery.However, recovering patients can't donate blood until at least 14 days after symptoms have subsided, to give the body time to clear viral particles."We don't want to transfuse the virus, just transfuse the antibodies," said.