Krishnamoorthi and Porter said they “had been made aware” that BARDA rejected proposals in early March for tests of immune globulin to prevent infection, and asked the agency to reconsider. They noted that the government is investing billions in vaccine research, but the largest study it has funded of immune globulin to prevent infection received just $34.6 million.

Immune globulin is derived from the blood plasma of people who have recovered from the coronavirus. It has been used for more than 100 years to treat a variety of diseases — including Ebola, polio and measles — with mixed success.

Tens of thousands of people in the U.S. have received convalescent plasma since the coronavirus outbreak began, but a small fraction of that has been through clinical trials. The federal government has not put money into the types of studies that would enable health care professionals to determine whether the treatment works.

Hospitals and academic researchers are conducting a handful of trials that could take months to produce results. But the government has spent $187 million on convalescent plasma since April — without knowing whether the treatment works.

Officials working on Operation Warp Speed, a Trump administration project to accelerate the development of Covid-19 vaccines and drugs, are also trying to set up a system in Florida to distribute convalescent plasma — similar to a program that hospitals, blood banks and patient activists established in New York City in April, according to two people who were on a conference call with the officials Friday.

Warp Speed officials are working on public service announcements encouraging Floridians to donate plasma, even though they expressed concern on the call that people might not want to participate if it became widely known that the administration is behind the effort, the two people said.

Chaim Lebovits, a plasma donor and New York shoe wholesaler, helped to organize a large plasma donation system in New York, and is now working on the Florida project. He said the plan is to send Florida convalescent plasma units stored in New York, as well as to set up grassroots drives in different communities and have medical providers to reach out to qualified donors of plasma.

Administration efforts have established the treatment is safe, with a $50 million investment from the Food and Drug Administration that went to Mayo Clinic centers across the country. But without a critical mass of data from clinical trials, the effectiveness of the treatment is unclear.

The lack of definitive evidence may not stop the FDA, a vocal supporter of convalescent plasma donations since March, from expanding access to the treatment.

Arturo Casadevall, a professor at Johns Hopkins Bloomberg School of Medicine who built a national system to link convalescent plasma donors and health providers, said he thinks the FDA will issue an emergency use authorization for the treatment. That would simplify its use for understaffed hospitals in states where cases are spiking, because they would no longer have to seek permission from the FDA to use the treatment outside of clinical trials.

Health experts say the National Institutes of Health should have stepped in and run a large clinical trial early on.

“Fauci’s shop should’ve done something,” said Nigel Paneth, an epidemiologist at Michigan State University, referring to the NIH’s top infectious disease expert, Anthony Fauci.

Paneth — who is running two convalescent plasma trials — and Casadevall said that the data so far on the efficacy of convalescent plasma is encouraging. Several small studies overseas have shown hints of efficacy, as did preliminary data from the Mayo Clinic study. But that data isn’t definitive.

The randomized, clinical trial results that will prove whether the treatment works are not expected to be released for several months, Casadevall added. Some trials are now starting to pool their data because they are having trouble enrolling patients, The Wall Street Journal reported.