Can blood from coronavirus survivors help other people fight the illness?

Doctors in New York will soon be testing the idea in hospitalized patients who are seriously ill.

Blood from people who have recovered can be a rich source of antibodies, proteins made by the immune system to attack the virus. The part of the blood that contains antibodies, so-called convalescent plasma, has been used for decades to treat infectious diseases, including Ebola and influenza.

“It’s kind of difficult scientifically to know how valuable it is in any disease until you try,” said Dr. David L. Reich, president and chief operating officer of the Mount Sinai Hospital, which will be using the treatment. “It’s not exactly a shot in the dark, but it’s not tried and true.”

Dr. Reich said it would be tried as a treatment for hospitalized patients who had a moderate form of the disease and had trouble breathing, but not for those who are in advanced stages of the disease.