Convalescent Plasma Therapy

What is convalescent plasma therapy?

Convalescent plasma therapy involves transfusing certain components from the blood of people who have had the virus and recovered into people who are very sick with the virus or people who are at high risk of getting the virus.

Convalescent plasma therapy is also known as passive antibody therapy, i.e. while it can immediately provide a person with antibodies to fight a virus, those antibodies only last a short period of time in the recipient’s body.

How does the therapy work?

Our body produces antibodies to fight the virus. The antibodies that attack the virus are secreted by immune cells and are found in plasma, or the liquid part of blood that helps the blood to clot when needed and supports immunity.

Once a person has had the virus and recovered, the antibodies produced will stay in their blood waiting to fight the same virus should it return. Those antibodies, when injected into another person with the disease, recognize the virus as something to attack.

History of convalescent plasma therapy

The use of convalescent plasma is not a new concept. It has been used since the 1800s.

The first trial was done in 1892 for treating diphtheria (a severe infection of the nose and throat) using blood serum initially. It was produced from animals who were infected with diphtheria, 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 (a bacterial illness that develops in people having strep throat). It was also used to treat pertussis (a highly contagious respiratory disease) until about 1970.

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 that includes measles, mumps, Argentine hemorrhagic fever, influenza, chickenpox, infections by cytomegalovirus, parvovirus B19 and, more recently, Middle East Respiratory Syndrome coronavirus (MERS-CoV), H1N1 and H5N1 avian flu, Ebola, and Severe Acute Respiratory Infections (SARI) viruses.

Effectiveness of convalescent plasma therapy

One possible explanation for the efficacy of convalescent plasma therapy is that the antibodies from convalescent plasma might suppress viraemia. Several studies showed a shorter hospital stay and lower mortality in patients treated with convalescent plasma than those who were not treated with convalescent plasma.

Uncertainties and limitations of convalescent plasma therapy

For any new infection, the potential risks of receiving convalescent plasma remain unknown. For instance, in the case of the dengue virus, getting convalescent serum makes the patient paradoxically worse, as it causes the virus to replicate. Other known complications that 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.

Although convalescent plasma is used as a therapeutic option for many viral infections, the efficacy, and safety of the therapy are yet to be proven in clinical trials.