Convalescent Plasma May Help Keep Some COVID Patients Out of the Hospital

Phlebotomist drawing blood sample for testing

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Key Takeaways

  • Transfusions of blood plasma from people who have recovered from COVID-19 (convalescent plasma) appear to lower the risk of hospitalization in some new COVID patients by as much as half (54%).
  • In the study, the transfusions were done on an outpatient basis within 9 days of a person testing positive for COVID.
  • If approved for use outside of clinical trials, convalescent plasma could be an alternative to monoclonal antibodies and other treatments for COVID.

A new study has found that early treatment with blood plasma donated by people who have recovered from COVID-19—called convalescent plasma—reduced new COVID patients’ risk of needing to be hospitalized by half.

In the trial, the researchers used plasma with high levels of antibodies against SARS-CoV-2, and the transfusions were done soon after someone got sick—within 9 days of when their symptoms started.

Preprint Study

The study was published online on medRxiv on December 21, 2021, but it has not yet been peer-reviewed.

What the Study Looked At

The researchers, led by a team at Johns Hopkins Bloomberg School of Public Health, conducted the study between June 3, 2020, and October 1, 2021.

A total of 1,181 patients at 24 sites in the United States took part in the trial. All of the participants were over the age of 18 and had had COVID-19 symptoms for fewer than 9 days, and none of them had needed to be hospitalized by the time that they were ready to get the transfusion.

During the study, half of the patients received convalescent plasma in their transfusion and the other half received a dose of plasma that had no COVID-19 antibodies as a placebo (or control).

Out of the 589 patients in the group that got the placebo plasma, 37 (6.3%) had to be hospitalized. In the group that received the convalescent plasma, 17 out of 592 (2.9%) had to be hospitalized.

According to the study’s findings, the convalescent plasma group’s relative risk of needing to be hospitalized for COVID was reduced by 54%.

Speaking at a webinar announcing the trial’s results, David Sullivan, MD, a professor of molecular microbiology and immunology at Johns Hopkins Bloomberg School of Public Health and co-lead author of the study, said that the findings showed “a clear difference. It’s clear daylight between the two curves, with a risk reduction of 54%.”

“Our findings suggest that this is another effective treatment for COVID-19 with the advantages being low cost, wide availability, and rapid resilience to the evolving SARS-CoV-2,” said Kelly Gebo, MD, MPH, a professor of medicine at the Johns Hopkins University School of Medicine and the co-lead of the study, during the same webinar.


The research did have a few limitations. First, the study was published online as a preprint and it has not yet has not been evaluated by other researchers to determine if there are any problems with the study’s methods or the findings (a process called peer review).

There are also a few other things to note about the study. For example, because of the timing of the trial, about 80% of participants were not vaccinated when they were enrolled. Out of the 54 patients who needed to be hospitalized, 53 had not received a COVID vaccine.

Sullivan also said that most of the plasma that was used in the study—90%—was collected in 2020 before variants like Delta and Omicron had started to circulate.

Why Use Convalescent Plasma?

According to Sullivan, the benefits of using convalescent plasma are that it is a low-cost and safe treatment and that it’s widely available. It also provides antibodies to fight the infection as soon as it is transfused.

Sullivan also explained that convalescent plasma has been used to treat infections in the past—for example, a 1937 study of convalescent plasma being used to treat pneumococcus type 1 pneumonia.

The treatment might also prove useful as we face more COVID variants in the future. Convalescent plasma has different naturally formed antibodies (polyclonal) to the SARS-CoV-2 virus. Monoclonal antibodies, which are made in the laboratory, consist of one or two types of antibodies to the virus.

Since convalescent plasma is polyclonal and adapts as the virus does, new supplies of plasma are expected to be useful against new variants of the virus, like Omicron. Monoclonal antibodies to new variants of the virus, on the other hand, take time to be made.

What Other Studies Showed

Research on convalescent plasma use in COVID patients has produced mixed results. In August, the Clinical Trial of COVID-19 Convalescent Plasma in Outpatients found that convalescent plasma was not effective against COVID-19 when it was given to patients within the first week after their symptoms appeared.

In early December, the World Health Organization (WHO) advised against using convalescent plasma as a treatment for COVID-19, except in clinical trials. Likewise, the use of convalescent plasma is not allowed by the Food and Drug Administration (FDA) for outpatient use except, again, in clinical trials.

At the webinar announcing the study’s results, Gebo said that the collection of convalescent plasma could be done on a larger scale if its use were to be approved. There are many potential donors of convalescent plasma (people who have had COVID-19 and recovered).

Gebo said that the research team has shared its data from the new study with both the FDA and the WHO.

What This Means For You

Convalescent plasma from people who have recovered from COVID-19 might help new COVID patients avoid the hospital. However, more research is needed and the treatment needs to be approved for more uses by the FDA.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Sullivan DJ, Gebo KA, Shoham S, et al. Randomized controlled trial for early outpatient COVID-19 treatment with high-titer convalescent plasma. medRxiv. Preprint posted online December 21, 2021. doi:10.1101/2021.12.10.21267485

  2. Korley FK, Durkalski-Mauldin V, Yeatts SD, et al. Early convalescent plasma for high-risk outpatients with COVID-19. N Engl J Med. 2021;385:1951-1960. doi:10.1056/NEJMoa2103784

By Valerie DeBenedette
Valerie DeBenedette has over 30 years' experience writing about health and medicine. She is the former managing editor of Drug Topics magazine.