title: Influenza vaccination reduces hemorrhagic stroke risk in patients with atrial fibrillation: A population-based cohort study.
abstract: OBJECTIVE
  The risk of hemorrhagic stroke in patients with atrial fibrillation (AF) is low but the consequences of its occurrence are extremely severe. In this study, we investigated the association of influenza vaccination with the risk of hemorrhagic stroke to develop an efficient strategy for reducing this risk in patients with AF.
  
  
  METHODS
  In this study, data were retrieved from the Taiwan National Health Insurance Research Database. The study cohort comprised all patients who received a diagnosis of AF (n=14,454) before January 1, 2005 (index date) and were followed until December 31, 2012. Propensity scores were calculated using a logistic regression model to determine the effects of vaccination by accounting for covariates that predict receiving the intervention (vaccine). A time-dependent Cox proportional hazard model was used to calculate the hazard ratios (HRs) for hemorrhagic stroke in vaccinated and unvaccinated patients with AF.
  
  
  RESULTS
  The study population comprised 6570 patients who did (2547 [38.77%]) and did not receive (4023 [61.23%]) influenza vaccination. The adjusted HRs (aHRs) for hemorrhagic stroke were lower in the vaccinated patients than in the unvaccinated patients (influenza season, noninfluenza season, and all seasons: aHRs=0.97 [0.59-1.60], 0.51 [0.30-0.87], and 0.72 [0.50-1.03], respectively).
  
  
  CONCLUSIONS
  Influenza vaccination exerts dose-response and synergistic protective effects against hemorrhagic stroke in patients with AF who have a high risk of hemorrhagic stroke (i.e., male sex, age≥75years, Charlson comorbidity index ≥3, and hypertension) and reduces the incidence of hemorrhagic stroke.
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan; Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Ju-Chi
authors.initials: JC
authors.lastname: Liu
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan.
authors.forename: Ta-Jung
authors.initials: TJ
authors.lastname: Wang
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan; Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Li-Chin
authors.initials: LC
authors.lastname: Sung
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan; Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Pai-Feng
authors.initials: PF
authors.lastname: Kao
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan.
authors.forename: Tsung-Yeh
authors.initials: TY
authors.lastname: Yang
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan.
authors.forename: Wen-Rui
authors.initials: WR
authors.lastname: Hao
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan.
authors.forename: Chun-Chao
authors.initials: CC
authors.lastname: Chen
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan.
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Hsu
authors.affiliation: Institute of Toxicology, College of Medicine, National Taiwan University, Taipei, Taiwan; Department of Radiation Oncology, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan; Department of Internal Medicine, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan; Department of Biotechnology, Hungkuang University, Taichung, Taiwan. Electronic address: szuyuanwu5399@gmail.com.
authors.forename: Szu-Yuan
authors.initials: SY
authors.lastname: Wu
mesh_terms: D000368:Aged; D001281:Atrial Fibrillation / Q000150:complications*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007252:Influenza Vaccines / Q000494:pharmacology*; D007251:Influenza, Human / Q000150:complications / Q000517:prevention & control*; D029521:Alphainfluenzavirus / Q000276:immunology; D020300:Intracranial Hemorrhages / Q000453:epidemiology* / Q000209:etiology; D008875:Middle Aged; D011159:Population Surveillance; D011379:Prognosis; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D015996:Survival Rate / Q000639:trends; D013624:Taiwan / Q000453:epidemiology; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines
keywords: Atrial fibrillation; Hemorrhagic stroke; Influenza vaccination