Mayo Clinic researchers and collaborators have found investigational convalescent plasma to be safe following transfusion in a diverse group of 20,000 patients. The findings - from the U.S. Food and Drug Administration's Expanded Access Program for COVID-19 - are reported in Mayo Clinic Proceedings.

The safety report assessed the seven days following transfusion for hospitalized patients between April 3 and June 11 who were deemed at risk of progressing to a severe or life-threatening condition. Nearly 40% of the patients were women; 20% African Americans; nearly 35% Hispanic and 5% Asian. Seven-day mortality rates declined to 8.6 % compared to 12% in a previous safety study of the first 5,000 transfused patients. Serious adverse events continued to be less than one percent.

"Our efforts to understand convalescent plasma continue," says Michael Joyner, M.D., principal investigator of the EAP at Mayo Clinic and lead author of the article. "We're optimistic but must remain objective as we assess increasing amounts of data."

This expanded safety report reveals a decline in mortality which appears contemporary with the more rapid availability of plasma for use, but the authors caution that this alone does not provide any evidence on effectiveness of convalescent plasma for treating COVID-19. Given the accelerating use of the therapy, research is now broadening its focus to determine indicators of efficacy. At this time, convalescent plasma therapy is the only antibody-based therapy for COVID-19.

"The 7000-plus physicians who are part of the program have done an exceptional job of offering convalescent plasma to a diverse group of patients, enrolling women as forty percent of the participants as well as significant numbers of patients who are of African American, Asian or Hispanic ethnicity," says researcher DeLisa Fairweather, Ph.D. "We hope recruitment of minority subjects continues to increase given the disproportionate burden these communities have faced with COVID-19."

The researchers say that while the mortality rate has decreased, the patients in the latter part of this study were less critically ill. They also say the decrease may be in part due to improved medical care based on increased knowledge during the pandemic and that more of the patients received the plasma earlier in their hospital treatment. They note that there was no system in place for delivering convalescent plasma in March and now there is sufficient donation to meet most of the demand. Also, as donors came forward more rapidly, it was more likely their plasma contained neutralizing antibodies.