In 1934, a doctor at a private boys’ school in Pennsylvania tried a unique method to ward off a potentially fatal measles epidemic. Dr. J. Roswell Gallagher extracted blood serum from a student who had recently recovered from a serious measles infection and began injecting plasma into 62 other boys who were at high risk of getting the disease.
Only three students eventually contracted measles and all were mild cases.
The method, although relatively new, was not new to science. In fact, the very first Nobel Prize in Physiology and Medicine was awarded in 1901 to Emil von Behring for his life-saving work in the development of a remedy for diphtheria, a particularly fatal bacterial infection in children. Its revolutionary treatment, known as diphtheria antitoxin, worked by injecting sick patients with antibodies taken from animals that had recovered from the disease.
READ MORE: Pandemics that have changed history
How convalescent plasma therapy works
Von Behring’s anti-toxin was not a vaccine, but the first example of a treatment method called “convalescent plasma” that has come back to life as a potential treatment for COVID-19. Convalescent plasma is blood plasma extracted from an animal or human patient who is “recovering” or who has recovered from an infection with a particular disease.
“Convalescent plasma has been used throughout history to cope with an infectious disease where people recover and there is no other therapy available,” says Warner Greene, director of the Center for HIV Cure Research at the Gladstone Institutes. “There must be something in their plasma, that is. an antibody – which helped them recover. “
Convalescent plasma interacts with the immune system differently than a vaccine. When a person is treated with a vaccine, their immune system actively produces their own antibodies that will kill any future encounter with the target pathogen. This is called active immunity.
Convalescent plasma offers what is called “passive immunity”. The body does not create its own antibodies, but “borrows” them from another person or animal that has successfully fought the disease. Unlike a vaccine, protection does not last a lifetime, but the antibodies borrowed can significantly reduce recovery times and even make the difference between life and death.
“Convalescent plasma is the coarsest of the immunotherapies, but it can be effective,” says Greene.
Plasma treatments cut Spanish flu deaths in half
WATCH: The Spanish flu was more deadly than the First World War
After von Behring’s antitoxin was distributed worldwide to treat diphtheria in 1895, doctors experimented with the same passive immunity technique to cure measles, mumps, polio, and flu.
During the 1918 pandemic flu epidemic known as “Spanish Flu “mortality rates have been cut in half for patients treated with blood plasma compared to those who have not been. The method seemed particularly effective when patients received antibodies in the early days of their infection, before their own immune systems had a chance to overreact and damage vital organs. In the 1930s, doctors like Gallagher effectively used convalescent plasma against measles.
Korean War Troops Saved By Plasma Treatment
In the 1940s and 1950s, antibiotics and vaccines began to replace the use of convalescent plasma to treat many outbreaks of infectious disease, but the old-fashioned method still proved useful during the Korean War when thousands of United Nations soldiers were struck by something called Korean Hemorrhagic Fever, also known as the Hantavirus. In the absence of any other treatment, field doctors have transfused convalescent plasma to sick patients and saved countless lives.
Greene says convalescent plasma has even been deployed against 21st century MERS outbreaks, SARS and Ebola, all new viruses that spread in communities without natural immunity, without a vaccine, and without effective antiviral treatment. Today, the best treatment for Ebola remains a pair of “monoclonal antibodies”, individual antibodies isolated from convalescent plasma and then artificially cloned in a laboratory.
READ MORE: The most heartbreaking battle in the Korean War
Fight COVID-19 with convalescent plasma
One of the most well-known modern uses of convalescent plasma is the production of antivenom to treat the bites of deadly snakes. Antivenom is made by injecting small amounts of snake venom into horses and allowing the horse’s immune system to produce antibodies that neutralize the poison. These equine antibodies are isolated, purified and distributed to hospitals as an antivenom.
In March 2020, doctors at Johns Hopkins University began testing convalescent plasma as a promising transitional treatment for COVID-19 as the search for a permanent vaccine continued. The advantage of convalescent plasma is that it can be taken from recovered patients using the same plasma separation technology used in blood banks.
“Everything is doable,” says immunologist Arturo Casadevall, lead researcher on the COVID-19 study, “but to do that, it takes effort, organization, resources … and people who have remissions of disease that can donate blood. ”
READ MORE: See all pandemic coverage here.