H1N1 Vaccine Associated With Small but Significant Risk of Guillain-Barre Syndrome

Guillain-Barre syndrome (GBS) is usually characterized by rapidly developing motor weakness and areflexia (the absence of reflexes). “The disease is thought to be autoimmune and triggered by a stimulus of external origin.

In 1976-1977, an unusually high rate of GBS was identified in the United States following the administration of inactivated ‘swine’ influenza A(H1N1) vaccines. In 2003, the Institute of Medicine (IOM) concluded that the evidence favored acceptance of a causal relationship between the 1976 swine influenza vaccines and GBS in adults.

Studies of seasonal influenza vaccines administered in subsequent years have found small or no increased risk,” according to background information in the article. “In a more recent assessment of epidemiologic studies on seasonal influenza vaccines, experimental studies in animals, and case reports in humans, the IOM Committee to Review Adverse Effects of Vaccines concluded that the evidence was inadequate to accept or reject a causal relationship.”

Image shows someone inserting a needle into a vaccine bottle.
Analysis of recent H1N1 vaccination data indicated a small but significant risk of GBS following influenza A(H1N1) vaccinations.

Philippe De Wals, M.D., Ph.D., of Laval University, Quebec City, Canada and colleagues conducted a study to assess the risk of GBS following pandemic influenza vaccine administration. In fall 2009 in Quebec an immunization campaign was launched against the 2009 influenza A(H1N1) pandemic strain. By the end of the year, 4.4 million residents had been vaccinated. The study included follow-up over the 6-month period of October 2009 through March 2010 for suspected and confirmed GBS cases reported by physicians, mostly neurologists, during active surveillance or identified in the provincial hospital summary discharge database. Immunization status was verified.

Over the 6-month period, 83 confirmed GBS cases were identified. Twenty-five confirmed cases had been vaccinated against 2009 influenza A(H1N1) 8 or fewer weeks before disease onset, with most (19/25) vaccinated 4 or fewer weeks before onset. Analysis of data indicated a small but significant risk of GBS following influenza A(H1N1) vaccination. The number of cases attributable to vaccination was approximately 2 per 1 million doses. The excess risk was observed only in persons 50 years of age or older.

“In Quebec, the individual risk of hospitalization following a documented influenza A(H1N1) infection was 1 per 2,500 and the risk of death was 1/73,000. The H1N1 vaccine was very effective in preventing infections and complications. It is likely that the benefits of immunization outweigh the risks,” the authors write.

Notes about this H1N1 and Guillain-Barre syndrome research

Read more about Guillain-Barre syndrome at the NIH page.

Funding: This study was funded by the Ministere de la Sante et des Services sociaux du Quebec and by the Public Health Agency of Canada-Canadian Institutes for Health Research Influenza Research Network.

Contacts:  Sylvain Gagné – JAMA and Archives Journals
Philippe De Wals – Université Laval
Source: American Medical Association press release
Image Source: Image adapted from an image in the public domain at Wikimedia Commons.
Original Research: Full research paper for “Risk of Guillain-Barré Syndrome Following H1N1 Influenza Vaccination in Quebec” by Philippe De Wals, PhD; Geneviève Deceuninck, MD; Eveline Toth, MSc; Nicole Boulianne, MSc; Denis Brunet, MD; Renée-Myriam Boucher, MD; Monique Landry, MD and Gaston De Serres, PhD in The Journal of American Medical Associations 11 July 2012 , 308(2):175-181, doi:10.1001/jama.2012.7342

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