WASHINGTON : A large study of 20,000 hospitalised COVID-19 patients who received transfusions of blood plasma from recovered people found the treatment was safe.The report, published in the journal Mayo Clinic Proceedings on Thursday, assessed the seven days following transfusion for hospitalised patients between April 3 and June 11 who were deemed at risk of progressing to a severe or life-threatening condition.Nearly 40 per cent of the patients were women; 20 per cent African Americans; 35 per cent Hispanic and 5 per cent Asian, the researchers said.Seven-day mortality rates declined to 8.6 per cent compared to 12 per cent in a previous safety study of the first 5,000 transfused patients, the researchers said.Serious adverse events.