title: Evaluation of Guillain-Barré Syndrome among recipients of influenza vaccine in 2000 and 2001.
abstract: BACKGROUND
  The 1976-1977 swine influenza vaccine was associated with an elevated risk of Guillain-Barré Syndrome (GBS), especially within 6 weeks after vaccination. A 2004 IOM report concluded that evidence was inadequate to accept or reject a causal relationship between subsequent influenza vaccine formulations and GBS. Studies published after the IOM report have been limited by passively reported data or lack of validation of coded diagnoses.
  
  
  OBJECTIVE
  To evaluate whether influenza vaccine is associated with GBS.
  
  
  METHODS
  Controlled observational study using national data from the Medicare program, which ensures a predominantly elderly population. People included had a Medicare claim for influenza vaccination during September-December in 2000 or 2001. Medical records were reviewed to classify definite, probable, or possible GBS (or not a case) using a standardized case definition. In a risk interval design, the incidence rate of GBS during Weeks 0-6 after vaccination (exposed period) was compared to Weeks 9-14 after vaccination (comparison period). Data collection occurred during 2003-2007, and analysis was conducted during 2007-2009.
  
  
  RESULTS
  Primary analysis included 22.2 million vaccinees, among whom 164 definite or probable GBS cases with onset during Weeks 0-6 or 9-14 were identified. The incidence rate ratio (IRR [95% CIs]) based on the GBS rate in the vaccine-exposed versus comparison periods, was 1.04 (0.76, 1.43) for combined years; 0.86 (0.52, 1.41) among people vaccinated in 2000; and 1.21 (0.79, 1.86) among people vaccinated in 2001. Secondary analysis additionally included 74 possible GBS cases; results were similar.
  
  
  CONCLUSIONS
  Overall, the results do not support an association between influenza vaccine receipt and GBS among the elderly for the years studied (2000-2001 and 2001-2002 formulations).
authors.affiliation: Office of Biostatistics and Epidemiology, Center for Biologics Evaluation and Research, Food and Drug Administration, Rockville, Maryland 20852, USA. dale.burwen@fda.hhs.gov
authors.forename: Dale R
authors.initials: DR
authors.lastname: Burwen
authors.forename: Robert
authors.initials: R
authors.lastname: Ball
authors.forename: Wilson W
authors.initials: WW
authors.lastname: Bryan
authors.forename: Hector S
authors.initials: HS
authors.lastname: Izurieta
authors.forename: Lawrence
authors.initials: L
authors.lastname: La Voie
authors.forename: Neville A
authors.initials: NA
authors.lastname: Gibbs
authors.forename: Rebecca
authors.initials: R
authors.lastname: Kliman
authors.forename: M Miles
authors.initials: MM
authors.lastname: Braun
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D020275:Guillain-Barre Syndrome / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D007252:Influenza Vaccines / Q000009:adverse effects*; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data; D012306:Risk; D014481:United States
chemical_list: D007252:Influenza Vaccines