Studies of convalescent plasma during the pandemic have shown it’s safe. But despite anecdotal evidence, no research has proven it’s effective against the coronavirus. Many patients who’ve received it have also had other medications, making it difficult to determine what therapy, if any, helped.

“It is unfortunate. We’re here in August, and we don’t have a rigorous response” to whether convalescent plasma works, Dr. Francis Collins, the director of the National Institutes of Health, said at a news briefing Tuesday.

In the same call with reporters, the nation’s top infectious disease expert, Dr. Anthony Fauci, underscored the importance of a placebo-controlled, randomized trial for the plasma.

“If that had been done, we would’ve had the answer to that right now,” said Fauci, director of the National Institute of Allergy and Infectious Diseases.