It may sound like back to the Stone Age but there's good scientific reason to try using survivors' blood, said Dr. Jeffrey Henderson of Washington University School of Medicine in St. Louis, who coauthored the FDA application with Casadevall and another colleague at the Mayo Clinic. When a person gets infected by a particular germ, the body makes specially designed proteins called antibodies to fight the infection. After the person recovers, those antibodies float in survivors' blood, specifically plasma, the liquid part of blood for months, even years. One of the planned studies would test if giving infusions of survivors' antibody-rich plasma to newly ill COVID-19 patients would boost their own body's attempts to fight off the virus. To see if it works, researchers would measure if the treatment gave patients a better chance of living or reduced the need for breathing machines. One caution: While regular plasma transfusions are a mainstay of medicine, rarely they can cause a lung-damaging side effect.