What is convalescent plasma?
Convalescent plasma (also called immune plasma or hyperimmune plasma) is blood plasma that a person who has recovered from a specific illness has donated for the goal of providing passive immunity to a person who currently has that specific illness. Convalescent plasma contains antibodies to the germ or virus that caused the illness, so a person who has that illness for the first time may receive the plasma to boost their ability to fight the pathogen.
The word “convalescent” describes anyone recovering from a disease.
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Can convalescent plasma therapy be used to treat COVID-19?
The U.S. Food and Drug Administration (FDA) has given emergency use authorization (EUA) for convalescent plasma therapy with high antibody levels (“high titer”) to help treat COVID-19 in people who are in the hospital and are in the early phase of the virus.
Based on scientific evidence available, the FDA has concluded that convalescent plasma may be effective in treating COVID-19 and that the known and potential benefits of the plasma therapy outweigh the known and potential risks.
Healthcare providers do not rely solely on convalescent plasma to treat cases of COVID-19.
What is plasma?
Plasma is the liquid portion of blood. Approximately 55% of your blood is plasma. The remaining 45% of your blood consists of red blood cells, white blood cells and platelets that are suspended in the plasma.
About 92% of plasma is water, but it also contains the following important components:
- Salt.
- Enzymes.
- Antibodies.
- Clotting factors.
- Albumin and fibrinogen, which are proteins.
When you donate blood, healthcare providers can separate these vital components from your plasma, which they can then concentrate into various products for treatment therapies. Convalescent plasma is one of those therapies. Healthcare providers are looking for certain antibodies in your plasma when you donate convalescent plasma.
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How does my immune system work?
Your immune system is a complex network of organs, white blood cells, antibodies and chemicals that work together to protect against infection, illness and disease.
When your immune system is working properly, it can tell which cells are yours and which cells and substances do not belong in your body. It activates, mobilizes, attacks and kills invader germs and pathogens that can make you sick.
Your immune system learns about germs after you’ve been exposed to them, and your body develops specialized blood proteins called antibodies to protect you from those specific germs. The antibodies kill the germs and prevent them from spreading to other cells in your body. It can take several days for your immune system to form antibodies against a specific germ that has entered your body for the first time.
Your immune system then “remembers” germs and pathogens that have entered your body and can respond and release specific antibodies to attack them right away if they enter your body again.
How does convalescent plasma therapy work?
The goal of convalescent plasma is to provide passive immunity — short-term immunity that results from introducing antibodies from another person. Healthcare providers may give convalescent plasma to people who have an illness that their immune system hasn’t responded to yet because they’ve never had the illness before.
A person who donates convalescent plasma has already had and recovered from the specific illness. Because of this, they have the antibodies needed to attack and kill the pathogen that causes the illness.
When a person who has a specific illness for the first time receives the convalescent plasma, the antibodies in the plasma bind to the disease-causing virus or bacterium and can potentially decrease or prevent the virus from entering into their cells and reproducing.
If you have not been previously exposed to or vaccinated against a pathogen, it can take as long as two to three weeks for your body to form antibodies against it. Providing antibodies through convalescent plasma has the potential to:
- Prevent illness.
- Shorten the length of time you’re sick.
- Lessen the severity of your illness.
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Who receives convalescent plasma therapy?
In general, people who are either early in their illness or who have weakened immune systems may be given the option of convalescent plasma therapy.
Scientists aren’t sure if convalescent plasma can benefit someone whose illness has progressed to organ damage or extreme inflammation, and healthcare providers don’t expect convalescent plasma to treat these complications. This is why providers suggest providing convalescent plasma in the early phase of the illness, especially for people who have weakened immune systems.
What conditions does convalescent plasma treat?
Scientists and healthcare providers use convalescent plasma primarily to try to treat people who have been exposed to new viruses. This is because the vast majority of the population does not have antibodies to a new virus outbreak, and scientists and providers may not know the best way to treat a new virus at first.
Providers have used convalescent plasma as a treatment therapy to provide passive immunity for several viral outbreaks, including:
- Coronavirus disease (COVID-19, or SARS-CoV-2).
- Severe acute respiratory syndrome-associated coronavirus (SARS-CoV).
- Spanish influenza A (H1N1).
- Avian influenza A (H5N1).
- 2009 pandemic influenza A (H1N1).
How effective is convalescent plasma therapy?
Each virus and illness is different, and each person is unique. Because of this, convalescent plasma therapy may benefit some people but have no effect on others. Scientists have not yet thoroughly studied just how effective convalescent plasma therapy is.
One study on the H1N1 (a type of flu) pandemic revealed that people who received influenza convalescent plasma might have had a reduction in the risk of death of more than 50% and had improvements in symptoms.
On the other hand, another study revealed that people who received convalescent plasma for Ebola virus disease did not have a significant improvement in survival. This could be because there were unknown levels of antibodies (most convalescent plasma therapy requires high levels of antibodies), and Ebola is generally more lethal than influenza. However, there is no way to know for sure based on the limits of the study.
