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While a vaccine for COVID-19 may still be years away, the U.S. Food and Drug Administration has taken steps to fast track a possible therapy for critically ill patients. The agency issued an emergency protocol Tuesday that would allow physicians to use convalescent plasma therapy.

The therapy, which dates back more than a century, ramps up a patient’s immune system by introducing antibodies from someone who has already been infected and successfully fought the virus. It is already being tested in a clinical trial setting, but the emergency protocol gives COVID-19 patients access to the investigational treatment outside of the trial setting.

Dr. Jennifer Binning

Dr. Jennifer Binning, virologist at Moffitt Cancer Center

“Our immune system is split into two major components with the innate immune response acting as a surveillance system for the body,” said Dr. Jennifer Binning, a virologist at Moffitt Cancer Center. “When it ‘sees’ a pathogen that does not belong, like a coronavirus, it sends the body a warning signal and activates an initial immune response. The adaptive part of our immune system then kicks in to generate antibodies to fight the infection and to establish immunological memory should the infection occur again.”

Treatment using convalescent blood products, such as plasma or serum, is not a new idea. Its earliest use dates to 1890, when physicians used blood serum to treat diphtheria. Plasma was used to treat scarlet fever and the flu starting in 1918. More recently the therapy has been tested for viral outbreaks when vaccines and treatment are not available, such as SARS, MERS and Ebola.

Previous studies found that the plasma therapy reduced symptoms and mortality for swine flu, SARS and MERS but had no effect on Ebola.

The FDA directed that emergency use of convalescent plasma therapy will be reserved for COVID-19 patients who are seriously ill or at risk of death. Doctors must request permission from the FDA to use the treatment. The agency says it will respond to written requests within four to eight hours, but if a patient needs immediate treatment, approval can be given over the phone.