Potential of Convalescent Plasma in Combatting Viral Outbreaks

Humanity recently faced two viral outbreaks with hantavirus on a cruise ship and a resurgence of Ebola in Africa. There are no vaccines or antiviral drugs available for these viruses, and treatment relies on supportive care. Discussions with medical experts often focus on quarantine, isolation, and the development of new therapies. However, convalescent plasma therapy, an existing treatment from survivors, is rarely mentioned.

When individuals recover from viral infections, they produce antibodies that can be transferred to other affected individuals. Use of convalescent plasma has been a part of infectious disease response since the early 20th century, such as during the 1918 influenza pandemic. More than 600,000 Americans received this therapy in the first year of the COVID-19 pandemic, saving numerous lives. In 2023, it showed promise during the West Nile virus outbreak in Israel.

While convalescent plasma has been used for past outbreaks of hantavirus and Ebola, its deployment was not optimal. Early use with high antibody levels is crucial for efficacy. Historically, evaluating its effectiveness was challenging as outbreaks ended quickly, preventing full studies. However, the COVID-19 pandemic was lengthy enough to conduct numerous clinical trials.

Convalescent plasma emerged as a validated therapy from the COVID-19 pandemic.

In 2024, COVID-19 convalescent plasma received FDA approval for use in immunosuppressed patients. It remains the sole antibody therapy for COVID. Despite its potential, convalescent plasma is often overlooked by medical professionals. Some cite difficulties in its use, especially in under-resourced areas due to the need for transfusion services, but more than 50 countries, including poorer ones, used it against COVID.

Concerns about standardization are raised, as each plasma unit varies in antibody content; however, standardization is possible. Some hesitation may stem from its status as an old therapy. Yet, familiarity with extensive evidence from COVID-19 could highlight its benefits. Convalescent plasma is a public good with minimal profit, relying on donors, health authorities, and physicians.

A key factor for successful deployment is the involvement of governmental health agencies. They can manage logistics for collecting, testing, and distributing plasma. During the COVID-19 pandemic, the FDA played a crucial role, significantly impacting lives.

Physicians often hesitate to recommend new therapies lacking evidence from randomized clinical trials, but such data is unavailable for newly emerging infections. Carefully maintained registries can provide essential information, as demonstrated by the FDA’s actions with convalescent plasma in 2020.

In past outbreaks, convalescent plasma was often reserved for critically ill patients. However, as an antiviral therapy, its effectiveness is maximized when used early in the disease course. For COVID-19, optimal results were seen in outpatients, reducing the risk of progression to hospitalization.

Public health authorities can now identify survivors willing to donate plasma, which can then be tested for antibodies against hantavirus and Ebola. One survivor’s donation can treat three patients. Convalescent plasma units can be frozen for future use, serving as a temporary therapy until vaccine and antiviral development progresses.

Arturo Casadevall, M.D., Ph.D., is a Bloomberg distinguished professor and chair of Molecular Microbiology and Immunology at Johns Hopkins School of Public Health. He was pivotal in deploying convalescent plasma for COVID and has authored over 100 papers on the topic.