In interviews, three federal health officials — Dr. Stephen M. Hahn, the former commissioner of the Food and Drug Administration; Dr. Peter Marks, a top F.D.A. regulator; and Dr. H. Clifford Lane, a clinical director at the National Institutes of Health — acknowledged that the evidence for plasma was limited.
“The data are just not that strong, and it makes it makes it hard, I think, to be enthusiastic about seeing it continue to be used,” Dr. Lane said. The N.I.H. recently halted an outpatient trial of plasma because of a lack of benefit.
Doctors have used the antibodies of recovered patients as treatments for more than a century, for diseases including diphtheria, the 1918 flu and Ebola.
So when patients began falling ill with the new coronavirus last year, doctors around the world turned to the old standby.
In the United States, two hospitals — Mount Sinai in New York City and Houston Methodist in Texas — administered the first plasma units to Covid-19 patients within hours of each other on March 28.
Dr. Nicole M. Bouvier, an infectious-disease doctor who helped set up Mount Sinai’s plasma program, said the hospital had tried the experimental treatment because blood transfusions carry a relatively low risk of harm. With a new virus spreading quickly, and no approved treatments, “nature is a much better manufacturer than we are,” she said.
As Mount Sinai prepared to infuse patients with plasma, Diana Berrent, a photographer, was recovering from Covid-19 at her home in Port Washington, N.Y. Friends began sending her Mount Sinai’s call for donors.