Reviving Convalescent Plasma: A Crucial Therapy for Viral Outbreaks

Recently, humanity faced two new viral outbreaks: hantavirus on a cruise ship and the return of Ebola in Africa. Currently, no vaccines or antiviral drugs exist for these viruses. The only available treatment is supportive therapy.

Medical experts often emphasize quarantine, isolation, and the need for new therapies. Yet, one proven therapy often goes unmentioned: convalescent plasma. Survivors of viral diseases produce antibodies that can be transferred to other affected individuals. Convalescent plasma has been used for infectious diseases since the early 20th century, including the 1918 influenza pandemic.

During the COVID-19 pandemic, over 600,000 Americans received convalescent plasma, saving many lives. In 2023, its use in the West Nile virus outbreak in Israel showed promising results. Past outbreaks of hantavirus and Ebola virus saw convalescent plasma use, yet its application was not optimal because efficacy depends on early use with sufficient antibody levels.

Historically, proving convalescent plasma’s efficacy was challenging as outbreaks often ended before thorough studies could occur. However, the COVID pandemic allowed for several clinical trials. Initial studies in other countries tested convalescent plasma in late-stage disease patients, where it showed little success. Subsequent trials confirmed its effectiveness when used early with sufficient antibody units.

In 2024, the FDA licensed COVID-19 convalescent plasma for immunosuppressed patients. Presently, it remains the only antibody therapy available for COVID.

Surprisingly, some medical professionals overlook convalescent plasma. Experts cite challenges in under-resourced areas due to required transfusion services for collection and screening. Despite this, over 50 countries, including poorer nations, used it against COVID. Concerns about standardization arise because each unit differs in antibody content, yet standardization by antibody amount is possible.

Perhaps reluctance stems from its status as an ‘old’ therapy. Like aspirin, known since ancient times, convalescent plasma persists as an effective option. A lack of familiarity may hinder its use, given its role in emergencies.

Convalescent plasma serves as a public good, lacking profit incentives. Pharmaceutical industries do not develop or promote it. Instead, it relies on donors, health authorities, transfusion services, and willing physicians.

Governmental health agencies are crucial for its success, managing logistics to collect, test, and deliver plasma units. During the COVID-19 pandemic, the FDA played a pivotal role in its deployment, saving lives.

Physicians often prefer evidence from randomized clinical trials before recommending therapies, yet new infectious agents lack such data. Carefully maintained registries can provide safety and efficacy data, as shown during the summer of 2020 with convalescent plasma.

Early COVID-19 approaches gave convalescent plasma to the sickest patients, which proved a mistake. Plasma, an antiviral therapy, works best early in the disease course, similar to other antiviral drugs. For COVID, optimal results occurred in outpatients, halving the risk of hospitalization.

Today, public health authorities can identify survivors, request plasma donations, and analyze antibody content for hantavirus and Ebola. One survivor’s plasma can treat three individuals. Units can be frozen for future use, providing interim therapy until vaccines or antiviral treatments emerge.

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. In 2020, he played a significant role in deploying convalescent plasma for COVID, authoring over 100 papers on the topic.