title: Risk of Guillain-Barré syndrome after exposure to pandemic influenza A(H1N1)pdm09 vaccination or infection: a Norwegian population-based cohort study.
abstract: Vaccinations and infections are possible triggers of Guillain-Barré syndrome (GBS). However, studies on GBS after vaccinations during the influenza A(H1N1)pmd09 pandemic in 2009, show inconsistent results. Only few studies have addressed the role of influenza infection. We used information from national health data-bases with information on the total Norwegian population (N = 4,832,211). Cox regression analyses with time-varying covariates and self-controlled case series was applied. The risk of being hospitalized with GBS during the pandemic period, within 42 days after an influenza diagnosis or pandemic vaccination was estimated. There were 490 GBS cases during 2009-2012 of which 410 cases occurred after October 1, 2009 of which 46 new cases occurred during the peak period of the influenza pandemic. An influenza diagnosis was registered for 2.47% of the population and the vaccination coverage was 39.25%. The incidence rate ratio of GBS during the pandemic peak relative to other periods was 1.46 [95% confidence interval (CI) 1.08-1.98]. The adjusted hazard ratio (HR) of GBS within 42 days after a diagnosis of pandemic influenza was 4.89 (95% CI 1.17-20.36). After pandemic vaccination the adjusted HR was 1.11 (95% CI 0.51-2.43). Our results indicated that there was a significantly increased risk of GBS during the pandemic season and after pandemic influenza infection. However, vaccination did not increase the risk of GBS. The small number of GBS cases in this study warrants caution in the interpretation of the findings.
authors.affiliation: Division of Epidemiology, Department of Health Registries, Norwegian Institute of Public Health, Kalfarveien 31, 5018, Bergen, Norway. Sara.Ghaderi@fhi.no.
authors.forename: Sara
authors.initials: S
authors.lastname: Ghaderi
authors.affiliation: Division of Epidemiology, Department of Genes and Environment, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Nina
authors.initials: N
authors.lastname: Gunnes
authors.affiliation: Division of Epidemiology, Department of Genes and Environment, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Inger Johanne
authors.initials: IJ
authors.lastname: Bakken
authors.affiliation: Institute Management and Staff, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Per
authors.initials: P
authors.lastname: Magnus
authors.affiliation: Division of Infectious Disease Control, Department of Vaccines, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Lill
authors.initials: L
authors.lastname: Trogstad
authors.affiliation: Institute Management and Staff, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Siri Eldevik
authors.initials: SE
authors.lastname: Håberg
mesh_terms: D005260:Female; D020275:Guillain-Barre Syndrome / Q000139:chemically induced* / Q000453:epidemiology*; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects*; D007251:Influenza, Human / Q000150:complications* / Q000453:epidemiology / Q000517:prevention & control; D008297:Male; D009664:Norway / Q000453:epidemiology; D058873:Pandemics; D011159:Population Surveillance / Q000379:methods*; D016016:Proportional Hazards Models; D012042:Registries; D012044:Regression Analysis; D012306:Risk; D014611:Vaccination / Q000009:adverse effects* / Q000706:statistics & numerical data
chemical_list: D007252:Influenza Vaccines
keywords: Guillain-Barré syndrome; Influenza; Norway; Pandemrix®; Registry; Vaccination