On Mar. 23, 2020, researchers at Washington University School of Medicine in St. Louis announced they were investigating whether transfusions of blood plasma from people who have recovered from COVID-19 can prevent or treat the disease.  Plasma and serum are both the clear fluid portion of blood, and both contain antibodies, but plasma also contains some other proteins lacking in serum. Serum therapy was used to treat small numbers of people during the SARS outbreak of 2002 and 2003.

In 1901, Emil von Behring was awarded the first Nobel Prize in Physiology or Medicine ‘for his discovery of serum therapy for diphtheria.’ During the 1918-1919 influenza pandemic, serum recovered patients was used to successfully treat acutely ill patients.