New research from Mayo Clinic has found that transfusing blood from people who have recovered from coronavirus to coronavirus patients is safe, though research is still needed on how effectively it treats the virus.

The Mayo Clinic began its convalescent plasma therapy program in April, as part of a national effort. In its study released Thursday, researchers followed 20,000 patients for seven days after receiving a transfusion. The mortality rate for these patients was 8.6 percent, an improvement from 12 percent in a smaller study. One percent of patients experienced serious adverse effects, such as lung injury or allergic reactions.

Nearly 40 percent of the patients were women, 20 percent were African Americans, 35 percent were Hispanic and 5 percent were Asian.

“We hope recruitment of minority subjects continues to increase given the disproportionate burden these communities have faced with COVID-19,” said researcher DeLisa Fairweather.

Researchers say the mortality rate decline between the two studies could be related to the fact that patients in later parts of the second study were less critically ill, and doctors were more equipped to treat COVID-19 than they were during the first study. Also, as more people recovering from the coronavirus became available — and encouraged early on — to donate, it was more likely that their blood contained antibodies for fighting the virus. 

“Our efforts to understand convalescent plasma continue,” said Dr. Michael Joyner, lead author of the study. “We’re optimistic but must remain objective as we assess increasing amounts of data.”

Recovered coronavirus patients interested in donating plasma can find more information here.