The Food and Drug Administration whipped up a fierce controversy Sunday when it decided to grant an Emergency Use Authorization, or EUA, for convalescent plasma to be used as a treatment for Covid-19. The decision came after many experts, including Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, had warned the agency there wasn’t enough evidence to fast-track approval for the novel treatment. The idea is that the plasma from people who have successfully withstood the virus contains antibodies, which can interfere with how a pathogen works or mark it as a target for elimination. That can then keep the disease in check or help the immune system eradicate it. It’s an approach that’s been used with varying degrees of success for other coronaviruses like SARS and MERS. But Covid-19 is a markedly different disease, and so far, no randomized control trials, the gold standard of evidence, on convalescent plasma have been completed.