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The risk of contracting Guillain-Barré Syndrome is greater after getting the flu, not the flu shot


Immunization remains the best defence again seasonal influenza, which causes an estimated 3 to 5 million cases of severe illness and 250,000 to 500,000 deaths each year worldwide. But the risk of contracting Guillain-Barré Syndrome (GBS), a serious but very rare condition from influenza vaccines remains a potential concern for large-scale immunization programs. GBS can cause paralysis, resulting in long-term disability and death; however, most patients recover from even the most severe cases of GBS. Researchers at the Institute for Clinical Evaluative Sciences (ICES) and Public Health Ontario (PHO) found that relative and absolute risks of GBS following seasonal influenza vaccination are lower than those of GBS following influenza illness.

“One case of GBS occurs with every one million flu shots administered, whereas a case of GBS occurs in every 60,000 influenza cases,” says Dr. Jeff Kwong, lead author of the study and scientist at ICES and PHO.

The study looked at people who developed GBS after receiving a flu shot or after seeing a doctor for influenza. The researchers looked at the risk in the six weeks after having a flu shot or an influenza illness compared with a later period which served as a baseline.

  • The risk of developing GBS within six weeks of a flu shot was 52 per cent higher than the usual risk (or one additional case of GBS per million flu shots).
  • The chance of developing GBS within six weeks of an influenza illness was nearly 16 times higher than the usual risk (or one additional case of GBS per 60,000 cases of influenza illness requiring medical attention).
  • The chance of developing GBS after influenza illness is far greater than that after receiving a flu shot.

“Overall, flu shots are generally safe and do more good than harm,” says Kwong.

Concern around contracting GBS after receiving the flu shot first surfaced in 1976. The swine-origin influenza immunization program in the U.S. was stopped because that vaccine increased the risk of GBS by four to eight times the baseline risk. However, this study shows the chance of developing GBS after influenza illness is far greater than after receiving a flu shot, and flu shots have other benefits by preventing influenza illness and serious complications from influenza infection.

The study “The risk of Guillain-Barré Syndrome following seasonal influenza vaccination and influenza healthcare encounters, a self-controlled study,” was published today in the journal, Lancet Infectious Diseases.

Authors: Jeffrey C. Kwong, Priya P. Vasa, Michael A. Campitelli, Steven Hawken, Kumanan Wilson, Laura C. Rosella, Therese A. Stukel, Natasha S. Crowcroft, Allison J. McGeer, Lorne Zinman and Shelley L. Deeks.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.

Public Health Ontario is a Crown corporation dedicated to protecting and promoting the health of all Ontarians and reducing inequities in health. Public Health Ontario links public health practitioners, front-line health workers and researchers to the best scientific intelligence and knowledge from around the world.

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Deborah Creatura
Communications, ICES
[email protected]
(o) 416-480-4780

Read the Journal Article