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What is convalescent plasma?
Convalescent plasma is a form of experimental treatment for Covid-19 that was first used in Wuhan, China. It involves the transfusion of plasma, a blood product, from a patient who has fully recovered from the infection to a patient who is infected but is getting worse.
Plasma is the liquid portion of blood and contains plenty of proteins including immune cells. Thus, convalescent plasma transfusion is based on the premise that if the immune cells of the fully recovered patient were able to fight off the infection successfully, transfusing them to a patient who is continuously deteriorating may lead to a replication of the results. That is, the deteriorating patient will also fully recover.
The premise is sound as immune cells in the human body have ‘memory’. This means that when the immune cells encounter a pathogen they have previously fought against, they recognize the pathogen and mount a similar reaction that overwhelmed the pathogen during first contact. This is similar to how vaccines works. A weakened pathogen is introduced into the human body and the immune cells respond by fighting off the weakened pathogen. When the vaccinated individual gets exposed to the pathogen they were immunized again, the immune cells recognize the pathogen and fight it off again successfully.
Convalescent plasma is extracted from the blood of recovered patients who simply donate blood. The donated blood is taken to an authorized lab where plasma can be extracted and stored appropriately. There is a long history of use of convalescent plasma from recovered patients in the treatment of infections including during the Ebola epidemic. It was most successfully used in the early 1900s to treat a bacterial infection known as diphtheria. The scientist who pioneered its use against diphtheria won a Noble Prize for his work.
Are there any risks associated with transfusion of plasma?
Transfusion of convalescent plasma, like other blood products, is generally safe. This is partly because of stringent FDA criteria when selecting a suitable donor as well as a suitable recipient. In addition, labs that handle blood products are highly regulated throughout the world. Even so, transfusion of blood products can lead to side effects to the recipient.
Allergic reactions and transmission of infections are the commonest. Transmission of infections is rare because, first and foremost, donated blood must be tested for common pathogens. In some centers, the donor has to fill a series of questionnaires and be tested against common infections such as hepatitis before being allowed to donate blood. Allergic reactions are also rare because of clinical protocols put in place to monitor patients receiving blood products. These patients are high priority and are monitored closely to catch any reactions early and reverse them accordingly.
Convalescent plasma and Covid-19
Convalescent plasma has proven especially useful in patients who have failed to respond to other forms of supportive and experimental treatment. Hence, it is often used as a last resort. Two case series published showed that Covid-19 patients who received convalescent plasma showed improved oxygenation in days to weeks. Some of the patients were successfully weaned off ventilators.
Currently, the FDA is allowing applications for use of convalescent plasma in individual patients. The FDA stipulates these patients need to sign a consent form indicating that they understand that this form of treatment is experimental. Finally, the FDA is engaging with researchers to develop a standard guideline for use of convalescent plasma in Covid-19 patients.
The National Covid-19 Convalescent Plasma Project is an ongoing initiative whose aim is to determine the efficacy and safety of convalescent plasma in severe covid-19. The key players are the FDA and St. John Hopkins Hospital. Under the initiative, 12,000 patients have received convalescent plasma. No formal results or guidelines have been published so far.
Convalescent plasma and pregnancy
Convalescent plasma is safe for pregnant women. Even so, pregnant women, like everyone else, are subject to all the risks associated with receiving blood products. Thus, the decision to transfuse a pregnant woman with convalescent plasma, while generally considered safe, is individualized. Currently, a study by Penn Medicine on the role of convalescent plasma in Covid-19 includes pregnant women as some of the study subjects. Finally, while pregnant women can receive blood products, they are not eligible donors. This is because pregnancy is often associated with anaemia.
Convalescent plasma is currently under investigation for its possible role in the fight against Covid-19. So far, it has been proven safe and modestly efficacious to the point where the FDA is allowing its use in select patients. Convalescent plasma is safe for pregnant women who can only receive the blood product but cannot donate.