A large study suggests convalescent plasma can help treat Covid-19 — maybe

The blood plasma from people who have recovered from Covid-19 may have therapeutic properties, according to a new study. Patients who received plasma transfusions within three days of a Covid-19 diagnosis had a seven-day death rate of 8.7%, while those who got it after four or more days had a mortality rate of 11.9%.

But the the Mayo Clinic study, which enrolled more than 35,000 patients, lacked a placebo arm — which has made it difficult for experts to interpret the data, STAT’s Matthew Herper and Damian Garde write.

“It raises the question of what strength of evidence is necessary to treat during a pandemic,” one Yale researcher told STAT. “The problem is we have yet to resolve what is sufficient evidence to change the treatment paradigm.”