Transfusions of blood serum from people who’ve recovered from covid-19 could help severe cases recover, according to a new study from China.

Plasma donation: The concept of using blood from survivors—or “convalescent plasma”—isn’t new, but it’s now being tried against covid-19 because there aren’t any drugs known to work. A survivor’s blood is charged up with antibodies against the virus. Give these to someone else, and they can give a temporary assist by interfering with the virus until that person mounts an immune response. 

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Positive result: The Chinese study, authored by scientists working for state-owned Sinopharm, wasn’t randomized, so benefits from plasma aren’t proven with certainty. But the 10 severely affected patients they treated with a half a Coke can’s worth of plasma seemed to do much better after three days.  In several of the patients the virus cleared up entirely, leading the authors to conclude that plasma “can serve as a promising rescue option” for severe covid-19 cases. The report follows a previous one from China involving five patients.

Recruiting now: US hospitals have been scrambling to find blood donors and are starting to try plasma transfusions, too. The American Association of Blood Banks has set up a web page so people recovered from covid-19 can find out where to donate blood. So has the Red Cross. People must be “fully recovered” to donate. The US Food and Drug Administration says people should wait 14 days after symptoms to donate.