Risk of Guillain-Barré syndrome after seasonal influenza vaccination and influenza health-care encounters: a self-controlled study

The Lancet Infectious Diseases
Sep 2013  Volume 13  Number 9   p725 – 822
http://www.thelancet.com/journals/laninf/issue/current

Risk of Guillain-Barré syndrome after seasonal influenza vaccination and influenza health-care encounters: a self-controlled study
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, Shelley L Deeks
http://www.thelancet.com/journals/laninf/article/PIIS1473-3099%2813%2970104-X/abstract

Summary
Background
The possible risk of Guillain-Barré syndrome from influenza vaccines remains a potential obstacle to achieving high vaccination coverage. However, influenza infection might also be associated with Guillain-Barré syndrome. We aimed to assess the risk of Guillain-Barré syndrome after seasonal influenza vaccination and after influenza-coded health-care encounters.

Methods
We used the self-controlled risk interval design and linked universal health-care system databases from Ontario, Canada, with data obtained between 1993 and 2011. We used physician billing claims for influenza vaccination and influenza-coded health-care encounters to ascertain exposures. Using fixed-effects conditional Poisson regression, we estimated the relative incidence of hospitalisation for primary-coded Guillain-Barré syndrome during the risk interval compared with the control interval.

Findings
We identified 2831 incident admissions for Guillain-Barré syndrome; 330 received an influenza vaccine and 109 had an influenza-coded health-care encounter within 42 weeks before hospitalisation. The risk of Guillain-Barré syndrome within 6 weeks of vaccination was 52% higher than in the control interval of 9—42 weeks (relative incidence 1·52; 95% CI 1·17—1·99), with the greatest risk during weeks 2—4 after vaccination. The risk of Guillain-Barré syndrome within 6 weeks of an influenza-coded health-care encounter was greater than for vaccination (15·81; 10·28—24·32). The attributable risks were 1·03 Guillain-Barré syndrome admissions per million vaccinations, compared with 17·2 Guillain-Barré syndrome admissions per million influenza-coded health-care encounters.

Interpretation
The relative and attributable risks of Guillain-Barré syndrome after seasonal influenza vaccination are lower than those after influenza illness. Patients considering immunisation should be fully informed of the risks of Guillain-Barré syndrome from both influenza vaccines and influenza illness.

Funding
Canadian Institutes of Health Research.