title: The pandemic influenza A (H1N1) 2009 vaccine does not increase the mortality rate of idiopathic interstitial pneumonia: a matched case-control study.
abstract: BACKGROUND
  Evidence regarding the mortality rate after administration of the pandemic influenza A (H1N1) 2009 vaccine on patients with underlying diseases is currently scarce. We conducted a case-control study in Japan to compare the mortality rates of patients with idiopathic interstitial pneumonia after the vaccines were administered and were not administered.
  
  
  METHODS
  Between October 2009 and March 2010, we collected clinical records in Japan and conducted a 1:1 matched case-control study. Patients with idiopathic interstitial pneumonia who died during this period were considered case patients, and those who survived were considered control patients. We determined and compared the proportion of each group that received the pandemic influenza A (H1N1) 2009 vaccine and estimated the odds ratio. Finally, we conducted simulations that compensated for the shortcomings of the study associated with adjusted severity of idiopathic interstitial pneumonia.
  
  
  RESULTS
  The case and control groups each comprised of 75 patients with idiopathic interstitial pneumonia. The proportion of patients who received the pandemic influenza A (H1N1) 2009 vaccine was 30.7% and 38.7% for the case and control groups, respectively. During that winter, the crude conditional odds ratio of mortality was 0.63 (95% confidence interval, 0.25-1.47) and the adjusted conditional odds ratio was 1.18 (95% confidence interval, 0.33-4.49); neither was significant. The simulation study showed more accurate conditional odds ratios of 0.63-0.71.
  
  
  CONCLUSIONS
  In our study, we detected no evidence that the influenza A (H1N1) 2009 vaccine increased the mortality rate of patients with idiopathic interstitial pneumonia. The results, however, are limited by the small sample size and low statistical power. A larger-scale study is required.
authors.affiliation: Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo City, Yamanashi, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yokomichi
authors.affiliation: Infection Control and Education Center, Nagasaki University, Nagasaki City, Nagasaki, Japan.
authors.forename: Shintaro
authors.initials: S
authors.lastname: Kurihara
authors.affiliation: Department of Health Promotion, National Institute of Public Health, Wako City, Saitama, Japan.
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Yokoyama
authors.affiliation: Department of Clinical Medicine (Biostatistics), School of Pharmacy, Kitasato University, Minato Ward, Tokyo, Japan.
authors.forename: Eisuke
authors.initials: E
authors.lastname: Inoue
authors.affiliation: Infectious Disease Surveillance Center, National Institute of Infectious Diseases, Shinjuku Ward, Tokyo, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Tanaka-Taya
authors.affiliation: Second Department of Internal Medicine, Nagasaki University School of Medicine, Nagasaki City, Nagasaki, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kono
authors.affiliation: Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo City, Yamanashi, Japan.
authors.forename: Zentaro
authors.initials: Z
authors.lastname: Yamagata
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D054988:Idiopathic Interstitial Pneumonias / Q000276:immunology* / Q000401:mortality*; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000009:adverse effects* / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology*; D007564:Japan; D008297:Male; D009026:Mortality; D016017:Odds Ratio
chemical_list: D007252:Influenza Vaccines