Convalescent plasma therapy

Antibody defense

To fight a virus, the immune system develops antibodies, proteins that bind to parts of the virus and impede the infection. When a person makes antibodies in response to an infection or upon getting a vaccine, it’s called active immunity. The initial ramp up to antibody production can take about a week or two, but once that has occurred, the immune system will be able to quickly respond to the next exposure to the virus. For some viruses and vaccines, active immunity can last decades or even lifelong.

Convalescent plasma, also called passive antibody therapy, is a type of passive immunity. It can provide antibodies immediately, but the proteins will last only for a short amount of time, weeks to possibly a few months.

 use of convalescent plasma is not a new concept. By giving patients plasma or serum from patients who have developed antibodies to a particular virus or bacteria, an infected patient is given a massive boost to their adaptive immune system, which confers passive immunity. It has been used since the 1800s.

The first valid trial was done in 1892 with diphtheria using blood serum initially. It was produced from animals who were infected with Diptheria, but soon whole blood or plasma recovered from donors with specific humoral immunity were identified as a possible source of specific antibodies of human origin. In the 1920s, it was used to treat scarlet fever. It was also used to treat and pertussis until about 1970. Horse serum was used to treat tetanus until the 1970s as well. 

During the Spanish influenza pandemic of 1918 convalescent plasma was used as a potential therapy with mixed results. It has been used in a variety of viral infections, although studies have been small and inconclusive. One success was the use of convalescent serum to treat Ebola virus.

For COVID-19, the potential risks of receiving convalescent plasma remain unknown. In the case of the dengue virus, getting convalescent serum makes the patient’s paradoxically worse, as it causes the virus to replicate. Other known complications include transfusion-associated reactions seen with any blood transfusion. There is also the possibility that other known or unknown pathogens could be introduced into the patients.