Demand for convalescent plasma has gone up in recent weeks, following the latest surge in coronavirus cases. Doctors and health officials across the country are desperately urging COVID-19 survivors to donate plasma, the yellowish, watery part of the blood that’s rich in proteins and antibodies. So-called convalescent plasma, from people who have recovered from a particular illness, has been used for more than 100 years to treat patients with all sorts of viruses, including influenza and Ebola. The hope is that plasma from a COVID-19 survivor, filled with antibodies against the virus, could boost the immune systems of those who are now sick, helping them to fight off the illness, too. “There is right now a lot of demand, and not as much supply,” Dr. Stephen Hahn, commissioner of the Food and Drug Administration, told NBC News. One doctor in Florida, for example, told him she’s ordering plasma infusions for COVID-19 patients as soon as they get to the emergency room.