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. This blog was updated on 10 July 2020 to incorporate the first update of this living systematic review.

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 on 14 May (updated 10 July), 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…

In the first version of this review (May 2020), 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…

In May 2020, the review authors found 47 ongoing studies investigating convalescent plasma treatment, of which 22 are randomized controlled trials, plus one study evaluating hyperimmune immunoglobulin. The plan is to 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.

The latest news (10 July 2020)

Since writing this blog, the review has been updated for the first time (published 10 July 2020). It now includes 20 studies with 5443 people. One of the studies is a randomized controlled trial with 103 people, of whom 52 received convalescent plasma while the rest received ‘standard care at time of treatment without convalescent plasma’. The trial was stopped early, with fewer participants than planned, because there were no more eligible people due to containment of the epidemic in Wuhan, and the review authors note that it is unclear to what extent this may bias the results. The evidence is all assessed as being ‘very low certainty’, so takes us no closer to answering important questions about the potential benefits and harms of this treatment for people with COVID-19.

The review authors also identified 98 ongoing studies, of which 50 are randomized trials. It’s clear that there is a scramble to produce evidence but is scientific rigour being sacrificed for speed? Let’s hope we get better quality studies in the next update.

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

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.


Piechotta  V, Chai  KL, Valk  SJ, 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 living systematic review. Cochrane Database of Systematic Reviews 2020, Issue 7. Art. No.: CD013600. DOI: 10.1002/14651858.CD013600.pub2.

Sarah Chapman has nothing to disclose.

Page last updated 10 July 2020

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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