The National Institutes of Health has expanded clinical trials investigating the use of convalescent plasma to treat COVID-19, based on promising but incomplete findings of earlier research.

“The evidence on convalescent plasma as a treatment for severe cases of COVID-19 is promising but incomplete. We need to carry out rigorous randomized control clinical trials to determine how this therapy can improve outcomes,” said NIH Director Francis S. Collins, MD, PhD, in a statement. “While the world waits for an effective vaccine, it is vital that we simultaneously expand the options for available treatments for those currently suffering from the worst effects of this disease.”

The first convalescent plasma trial in the U.S. began in April at NYU Langone Health in New York, in collaboration with Albert Einstein College of Medicine and Yale University, New Haven, CT. According to the NIH statement, the researchers expect to enroll 1,000 adults who are hospitalized with respiratory symptoms related to the virus.

A second trial, also launched in April, is run by researchers at Vanderbilt University Medical Center in Nashville, TN. The trial expansion will add 50 additional trial sites.

What is convalescent plasma?

People who recover from a viral infection usually are left with antibodies against the virus. When they are exposed to the virus again, their body recognizes it and either keeps the virus from taking over again, or they limit the extent of the illness. Using convalescent plasma goes back to when physicians were learning how to treat polio, and it’s also been used to treat hepatitis and other viruses.

Now, researchers take blood from COVID-19 survivors and remove the plasma – a straw-colored fluid, which contains the antibodies. This plasma is then given to patients who are ill with COVID-19.

Researchers don’t yet know how effective convalescent plasma is, so further study is needed.