Convalescent plasma to treat people with COVID-19: the evidence so far

Sarah Chapman blogs about the latest Cochrane rapid review produced in response to the COVID-19 pandemic, looking at the evidence on convalescent plasma as a possible treatment for COVID-19.

With an urgent need for evidence to help those making health decisions in these unparalleled times, one of the things Cochrane is doing in response is to produce rapid reviews. These are simplified systematic reviews that can be done in a few weeks to produce timely evidence for decision-making. The latest of these, published yesterday, brings together the evidence on convalescent plasma as a possible treatment for people with COVID-19.

What is convalescent plasma?

Plasma is a liquid that makes up about half of your blood volume. After a person has recovered from an infection (this is the convalescent bit), their blood contains antibodies that help fight infection. Some people who have fully recovered from an infection can donate plasma (as with blood donation, there are reasons why they might not be able to). Randomized trials are being done to investigate the potential benefits or harms of using plasma from people who have recovered from COVID-19 to treat people who are currently ill with it.

Convalescent plasma has been used in the past to effectively treat infections where there were no drug treatments or vaccines, such as diptheria and polio. Evidence on whether it helps treat severe respiratory infections has been mixed and there are potential harms too, such as allergic reactions.

So this has potential as a treatment for COVID-19 but we need to know what evidence there is on the benefits and risks.

What is the evidence from the Cochrane Rapid Review?

The review authors looked for studies investigating convalescent plasma or hyperimmune immunoglobulin (prepared from convalescent plasma) for people with COVID‐19, without any limits on age, ethnicity, gender or disease severity.

The disappointing news…

There were only 8 studies to include, with 32 people who received convalescent plasma. As well as there being very few people in the studies, they weren’t randomized controlled trials, which would give us more reliable evidence. None of the studies compared people receiving convalescent plasma with people who did not. There were other problems with the studies too, and the review authors note that it’s not possible to know whether the results reflect the natural history of the disease (the course the illness would take in an individual without treatment), the convalescent plasma treatments, or other treatments they were having at the same time.

The evidence here was assessed by the review authors as being ‘very low certainty’ and the bottom line is that the effectiveness and safety of convalescent plasma treatment for people with COVID-19 remain uncertain.

But that’s not the end of the story.

The better news…

The review authors found 47 ongoing studies investigating convalescent plasma treatment, of which 22 are randomized controlled trials, plus one study evaluating hyperimmune immunoglobulin. They will update this review as a ‘living systematic review’, searching for new evidence every month and adding it to the review. We will hope to see more reliable results as this evidence is added.

On this page, which is constantly updated, you can stay informed about Cochrane content relating to the coronavirus (COVID-19) pandemic and the various related activities that Cochrane is undertaking in response.

Take-home points

A Cochrane rapid review with 8 very small studies shows that the effectiveness and safety of convalescent plasma for people with COVID-19 are uncertain.There were no completed randomised controlled trials (RCTs) to include but the review authors found 48 ongoing studies, including 22 RCTs.The review will be updated as a ‘living systematic review’, based on monthly searches for new evidence. The results are likely to change.

Join in the conversation on Twitter with @CochraneUK @SarahChapman30 or leave a comment on the blog. Please note, we cannot give medical advice and we will not publish comments that link to commercial sites or appear to endorse commercial products.


Valk  SJ, Piechotta  V, Chai  KL, Doree  C, Monsef  I, Wood  EM, Lamikanra  A, Kimber  C, McQuilten  Z, So-Osman  C, Estcourt  LJ, Skoetz  N. Convalescent plasma or hyperimmune immunoglobulin for people with COVID‐19: a rapid review. Cochrane Database of Systematic Reviews 2020, Issue 5. Art. No.: CD013600. DOI: 10.1002/14651858.CD013600.

Sarah Chapman has nothing to disclose.



Sarah Chapman

About Sarah Chapman

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Sarah's work as a Knowledge Broker at Cochrane UK focuses on disseminating Cochrane evidence through social media, including Evidently Cochrane blogs, blogshots and the ‘Evidence for Everyday’ series for nurses, midwives, allied health professionals and patients. A former registered general nurse, Sarah has a particular interest making evidence accessible and useful to practitioners and to others making decisions about health. Before joining Cochrane, Sarah also worked on systematic reviews for the University of Oxford and the Royal College of Nursing Institute, and obtained degrees in History from the University of Oxford and in the history of women’s health and illness in early modern England (MPhil., University of Reading).

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