Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Cochrane is producing a series of reviews to help decision makers respond to the COVID-19 pandemic. In May 2020, we published our rapid review of the effects of convalescent plasma and hyperimmune immunoglobulin and we asked its lead author, Sarah Valk from the Center for Clinical Transfusion Research at Sanquin Blood Supply in the Netherlands, to tell us what they found.

Sarah: Convalescent plasma and hyperimmune immunoglobulin, which come from patients who have recovered from the infection, have been used in the past to treat a variety of infections when no other effective treatments are available. They were used in previous outbreaks of severe viral respiratory infections, such as influenza and Severe Acute Respiratory Syndrome, or SARS, and may reduce the risk of death. 
The hope is that convalescent plasma would treat COVID-19 disease through a process called passive immunization, by supplying virus-binding antibodies that would help clear viral particles. This is most likely to occur when treatment is given early after infection. Although convalescent plasma and hyperimmune immunoglobulin treatment are thought to be generally safe, adverse events can occur. So, it’s important to know whether they are an effective and safe treatment for people with COVID-19, and we brought together the evidence to try to assess this.
We searched for studies from anywhere in the world, including participants of any age, gender or ethnicity, who had mild, moderate or severe COVID-19. We were looking for the effects on a variety of patient outcomes, including survival, clinical improvement and adverse outcomes. We found eight studies with a total of 32 participants who had received convalescent plasma. There were no studies of hyperimmune immunoglobulin and none of the included studies had a control arm. 
All 32 participants in the studies were alive at the end of follow-up and most of those with severe disease had clinically improved at final follow-up. However, not all of them had been discharged from hospital by then. It’s also not clear whether their improvement was related to the convalescent plasma, another treatment, or simply the natural progression of the disease. This is why the absence of a control arm, that would allow us to assess these factors, is such a problem. There was one serious adverse event, with one participant experiencing a severe allergic reaction.  
In summary, the information from the studies that were available in late April 2020 means that we remain very uncertain about the effectiveness and safety of using convalescent plasma for people with COVID-19. Despite extensive searching, we were only able to include very low-quality evidence, from small uncontrolled studies, in which the participants received many other treatments. Different outcome measures were reported and we cannot know if recovery was due to the treatment or the natural course of the disease.
However, this field is changing rapidly. We identified approximately 50 on-going studies, of which 22 are randomized trials and, so, we will be updating this review periodically, as a 'living systematic review', so that it reflects the most current, available evidence.

Monaz: Thanks Sarah. If you’d like to read this rapid review, and to watch for its updates as the results of the ongoing studies become available, just go online to Cochrane Library dot com and search 'convalescent plasma and COVID-19'.