Convalescent Plasma Therapy for the Treatment of COVID-19: A Review of Clinical Effectiveness

Key Message

Convalescent plasma (CP) therapy is an intervention in which plasma collected from convalescent or recovered patients is used to treat certain infectious diseases. The purpose of this report is to summarize the evidence regarding the clinical effectiveness of CP therapy for the treatment of coronavirus disease (COVID-19).

In Canada, as of July 2021, CP therapy for COVID-19 is available only as an investigational drug treatment.

Nine randomized controlled trials and 28 non-randomized studies were included in this report. The included studies had several methodological limitations, unclear reporting, high heterogeneity, and limited generalizability to Canadian settings; overall, the evidence was of low-to-moderate quality.

There were mixed findings regarding a survival benefit associated with CP therapy compared to standard care or placebo (15 studies found no significant effects and 13 studies found favourable effects on mortality with CP). Given the limitations of the evidence as aforementioned, the potential survival benefit is unclear.

Whether CP was more effective than standard care or placebo for other outcomes (e.g., clinical improvement, disease progression, viral clearance, requirement for supplemental oxygen or other respiratory support such as mechanical ventilation, or duration of hospital stay) was unclear. In some studies, there were no significant differences between CP and standard care alone; in others, CP appeared to be comparatively favourable and, in a few instances, CP was comparatively unfavourable (e.g., 1 study for the outcome duration of hospitalization). However, because of the limited quality of the evidence, the comparative clinical effectiveness remains inconclusive.

CP therapy may be less effective than remdesivir or other active therapies in terms of mortality, requirement for O2 supplementation, and duration of hospitalization, as observed in 2 non-randomized studies of limited quality. Evidence from a non-randomized study of limited quality showed that that CP therapy and tocilizumab were equally effective in improving the clinical status of patients.

The incidence of adverse events was similar between patients treated with CP therapy or standard care alone in the few studies in which adverse events were assessed in patients who received either treatment. Adverse events were reported in 30 studies and were relatively infrequent. The most common adverse events in patients who received CP were fever and allergic reactions. Most of the included studies did not report whether there were adverse events in the control groups (e.g., patients who received standard care, remdesivir, or other medications).

This report includes a list of ongoing clinical trials that could provide additional evidence regarding the clinical effectiveness of CP therapy for COVID-19.

This report was conducted as a living review from May 2020 until July 2021. This is the final version of this report. A list of ongoing clinical trials is provided in Appendix 6. Key information regarding each version of this report can be found in Appendix 7.