Convalescent plasma is the liquid portion of blood from a person who has recovered from an infectious disease. It contains antibodies that the donor’s immune system created to fight the specific pathogen. The purpose of this plasma is to transfer these antibodies to a sick individual, giving their body a temporary boost to fight the infection while their own immune system responds.
Understanding How Convalescent Plasma Works
The therapeutic action of convalescent plasma provides passive immunity, which involves borrowing protective proteins from another source, unlike active immunity where the body produces its own. When a person is infected, their immune system can take weeks to generate specific antibodies. This delay can be dangerous with new or aggressive diseases.
A transfusion from a recovered donor provides a direct infusion of antibodies that can immediately target the pathogen. One mechanism is viral neutralization, where antibodies bind to virus particles, blocking them from entering the recipient’s cells and replicating. This action helps lower the body’s overall viral load.
Beyond direct neutralization, the antibodies can engage other parts of the recipient’s immune system. They can mark pathogens for destruction by other immune cells through processes like antibody-dependent cellular cytotoxicity. The plasma may also contain other components that help modulate the inflammatory response, which can become overactive in severe infections.
Historical and Modern Uses of Convalescent Plasma
The use of convalescent plasma is over a century old, serving as a defense against infectious diseases before antibiotics and vaccines were widespread. It was employed during the 1918 Spanish flu pandemic, where early administration was associated with reduced mortality. Throughout the 20th century, this therapy was used to treat infections like measles, mumps, and pneumococcus pneumonia.
With the rise of antiviral drugs and vaccines, the use of convalescent plasma became less common. It has re-emerged during outbreaks of new infectious diseases, such as the SARS epidemic in 2003. In that instance, early treatment was linked to better patient outcomes.
More recently, convalescent plasma has been used under emergency protocols for diseases like Ebola, MERS, H1N1 swine flu, and COVID-19. During the initial phases of the COVID-19 pandemic, health authorities issued emergency use authorizations for its use, especially for patients with weakened immune systems. This pattern highlights its role as a bridge therapy while more definitive treatments are developed.
From Donation to Transfusion
The process begins with qualifying suitable donors. To be eligible, a person must:
- Have a confirmed diagnosis of recovery from the specific infectious disease.
- Be symptom-free for a designated period.
- Meet standard blood donation health requirements.
- Have blood containing a high concentration (titer) of specific antibodies.
Once a donor is approved, plasma is collected via plasmapheresis. During this procedure, an automated machine draws the donor’s blood and separates the plasma from other components like red blood cells. The plasma is collected, while the other blood components are returned to the donor. This method allows for a larger volume of plasma to be collected more frequently than a standard whole blood donation.
After collection, the donated plasma is screened for blood-borne pathogens like HIV and hepatitis to ensure safety. Before transfusion, the recipient is matched with a compatible plasma unit based on their blood type. The plasma is then administered intravenously over one to two hours in a hospital setting.
Evaluating Convalescent Plasma Treatment
The effectiveness of convalescent plasma therapy is influenced by several factors. A primary determinant of success is the timing of administration. Evidence suggests the treatment is more beneficial when given early in the course of an illness, before the patient develops severe symptoms or organ damage.
Clinical trial results for convalescent plasma have been mixed, especially during the COVID-19 pandemic. While some early, smaller studies suggested a benefit, larger randomized controlled trials often found it did not significantly reduce mortality or the need for mechanical ventilation in hospitalized patients. However, its use in specific populations, such as those with compromised immune systems, remains an area of interest.
The treatment is considered safe, but like any blood product transfusion, it carries some risks. Potential adverse effects include allergic reactions, transfusion-associated circulatory overload (TACO), and transfusion-related acute lung injury (TRALI). Regulatory bodies like the FDA have granted and revised Emergency Use Authorizations (EUAs) for convalescent plasma based on evolving scientific evidence, reflecting its status as a treatment with a continually defined role.