In 1976, vaccination with the swine flu vaccine was associated with a small risk of developing Guillain Barre Syndrome (GBS), approximately 1 additional case per 100,000 people who received the swine flu vaccine, which was slightly higher than the background rate for GBS.
Since then, numerous studies have been done to evaluate if other flu vaccines were associated with GBS. In most studies, no association was found, but two studies suggested that approximately 1 additional person out of 1 million vaccinated people may be at risk for GBS associated with the seasonal influenza vaccine.
It is important to keep in mind that severe illness and possible death can be associated with influenza, and that vaccination is the best way to prevent influenza infection and its complications.
References
P. Haber, et al. "Guillain-Barre' Syndrome Following Influenza Vaccination."JAMA. 2004;292:2478-2481.
Stowe J, et al. Investigation of the temporal association of Guillain-Barré syndrome with influenza vaccine and influenza-like illness using the United Kingdom General Practice Research Database. Am J Epidemiol 2009;169:382-8.
