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Harnessing the Power of Convalescents for Severe Viral Infections

Amesh A. Adalja, MD, FACP, FACEP, August 1, 2014
 
The use of convalescent serum has sometimes been advocated for the treatment of acute severe viral diseases for which no specific countermeasure exists. This raises the question of whether these treatments are safe and effective. A new British study partially answers the question. 
 
During an outbreak of a new severe viral disease (such as MERS), there would most likely be no ready-to-use antiviral available for treatment. When confronting a disease with high morbidity and mortality rates, physicians would likely feel compelled to find some means to influence the clinical course other than supportive care. One potential approach is to harvest antibodies from the serum of survivors of a previous infection. Using convalescent sera seems an attractive and natural approach when no other is available. However, the use of such an approach has been limited by a lack of effectiveness data. To further explore the use of these treatments, a team from the UK recently published a systematic review and meta-analysis assessing the effectiveness of convalescent sera and hyperimmune immunoglobulin for the treatment of severe viral respiratory infections.
 
SARS-CoV, Influenza Included
 
The authors identified 32 studies of hospitalized patients infected with influenza or SARS who were administered convalescent plasma, serum, or hyperimmune immunoglobulin. 
 
Overall, the analysis consistently revealed mortality benefits—given caveats about the inclusion of biased studies—from the use of convalescent sera. This benefit was seen with SARS, 2009 H1N1 influenza, H5N1 influenza, and 1918 H1N1 influenza. In an exploratory meta-analysis restricted to comparative studies, convalescent plasma or serum was found to confer a statistically lower mortality rate, with an impressive pooled odds ratio of 0.25. 
 
Other analyses revealed decreased hospital lengths of stay and viral loads in treated SARS patients. No major adverse reactions were detected. 
 
Routine Use of Convalescent Sera? 
 
This article raises interesting questions regarding how best to manage patients in a scenario when no approved specific treatments are available. The history of convalescent therapies is one that stretches at least back to the 1918 influenza pandemic, and these therapies have been employed successfully since that time. While using convalescent serum therapy may be attractive as a targeted approach to treatment, the rate-limiting step may be the fact that the convalescent serum must first be available and then adequately screened and processed. Future studies, based on the findings described in this article, should not only include randomized controlled trials but also try to develop a mechanism whereby serum and plasma from survivors can be made readily available during outbreaks of severe viral respiratory diseases.
 
Reference
  1. Mair-Jenkins J, Saavedra-Campos M, Baillie K, et al. The effectiveness of convalescent plasma and hyperimmune immunoglobulin for the treatment of severe acute respiratory infections of viral aetiology: a systematic review and exploratory meta-analysis. J Infect Dis 2014. http://jid.oxfordjournals.org/content/early/2014/07/16/infdis.jiu396.abstract. Accessed July 15, 2014.