Recovered coronavirus patient Cai Taoying (R), who is also a nurse from Hankou Hospital, holds a certificate for blood donation while donating plasma at Wuhan Blood Center in Wuhan, capital of central China's Hubei Province, Feb. 17, 2020. Cured patients who were infected with COVID-19 are called upon to donate plasma as initial results had indicated the effectiveness of convalescent plasma-derived therapeutic products in curing infected patients in severe and critical conditions. Some recovered patients regard the donation as a way to pay back to the society after they received timely and effective treatment. (Xinhua/Cai Yang)