Very small risk of Guillain-Barré Syndrome following flu vaccination

Although previous research has been inconclusive, new findings from the Institute for Clinical Evaluative Sciences (ICES) suggest a very small increased risk of developing the potentially disabling neurological disorder Guillain-Barré syndrome (GBS)[1] after receiving the flu vaccine. However, researchers speculate that in patients at high risk of complications from the flu, that the benefits of vaccination likely far outweigh this risk.

“While we have estimated that, among people who get the flu shot, about 1-2 people per million will develop GBS, it’s important to consider this finding in the context of the benefits of the vaccine,” said Dr. David Juurlink, ICES scientist and the study’s lead author.

While the study did not examine the benefits of vaccination, the study’s authors note that “during flu season every year, 10-16% of people get the flu and thousands are hospitalized or die from it.”

In this study, investigators tracked adults vaccinated for influenza during the months of October and November (the peak months for influenza vaccinations) between April 1, 1992 and March 31, 2004, and examined the number of vaccinated people who were hospitalized for GBS after receiving the flu vaccine.

In a second analysis, the study authors also determined whether the implementation of Ontario’s universal influenza immunization program in October 2000 was associated with a subsequent increase in GBS hospital admissions.

In addition to the finding that just 1-2 people per million vaccinated will develop GBS, the study also showed that there was no statistically significant increase in GBS hospital admissions after the introduction of Ontario’s universal influenza immunization program in 2000.

“Flu vaccination is only one of many potential causes of GBS, and given the small individual risk associated with the vaccine, the decision to be vaccinated should be primarily based on its potential benefits,” said Dr. Kumanan Wilson, associate professor in the Department of Medicine at the University of Toronto and the study’s senior author.

"However, it’s still important for individuals who receive the flu vaccine to be advised of the potential risk of GBS, particularly in light of the serious consequences of the illness.” Dr. Wilson adds that the study’s findings also suggest that “it would be prudent to implement active surveillance for GBS as an essential component of any mass vaccination program.”

The study, “Guillain-Barré syndrome after influenza vaccination in adults: a population-based study”, is in the November 13, 2006 issue of the Archives of Internal Medicine.

Author affiliations: ICES (Drs. Juurlink, Stukel, Kwong, and Manuel); Departments of Medicine (Drs. Juurlink, McGeer, Moineddin, and Wilson), Health Policy, Management and Evaluation (Drs. Juurlink, McGeer, and Wilson), and Public Health Sciences (Drs. Upshur, Kwong, and Manuel), University of Toronto; Department of Microbiology, Mount Sinai Hospital (Dr. McGeer); Primary Care Research Unit, Sunnybrook Health Sciences Centre (Dr. Upshur); Toronto General Research Institute (Dr. Wilson)

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.

FOR FURTHER INFORMATION, PLEASE CONTACT:

• Julie Dowdie
• Media Relations Officer, ICES
• (416) 480-4780 or cell (416) 432-8143

[1] Guillian-Barré syndrome (GBS) is a potentially debilitating neurological disorder than can cause symptoms ranging from muscle weakness through to complete paralysis, but most people recover from it.