title: Annual influenza vaccination in community-dwelling elderly individuals and the risk of lower respiratory tract infections or pneumonia.
abstract: BACKGROUND
  Influenza vaccination has been associated with a reduction in the number of hospitalizations for respiratory conditions in elderly persons over the period from 1996 to 2002. Little is known, however, about the effect of influenza vaccination on the whole range of severity of respiratory tract infections.
  
  
  METHODS
  We investigated the effect of annual influenza vaccination on the occurrence of lower respiratory tract infections (LRTIs) in community-dwelling elderly individuals. From 1996 to 2002, we performed a population-based cohort study, using the computerized Integrated Primary Care Information database in the Netherlands, of community-dwelling subjects who were 65 years or older on January 1 of the year of study entry. For each year, the individual cumulative exposure to influenza vaccination since study entry was computed. We compared the risk of LRTI after a first vaccination or revaccination with the risk for no vaccination using a time-varying multivariate Cox proportional hazard model, adjusted for age, sex, smoking, and underlying disease.
  
  
  RESULTS
  In the study population of 26 071 subjects, 3412 developed LRTIs during follow-up. During the influenza epidemic periods, a first vaccination did not reduce risk for LRTI. In the total population, the hazard ratio following a first vaccination was 0.86 (95% confidence interval [CI], 0.71 to 1.05); in the population without or with comorbidity, these ratios were 0.90 (95% CI, 0.56 to 1.45) and 0.83 (95% CI, 0.66 to 1.04), respectively. During epidemic periods, revaccination reduced risk of LRTI by 33% (95% CI, 8% to 52%) in individuals without comorbidity. In individuals with comorbidity, the risk reduction of 5% was nonsignificant (95% CI, -10% to 18%).
  
  
  CONCLUSIONS
  In this study, annual influenza revaccination was associated with a reduction in LRTI in community-dwelling elderly individuals.
authors.affiliation: Pharmacoepidemiology Unit, Department of Internal Medicine and Epidemiology, Erasmus University Medical Center, Rotterdam, the Netherlands. ac.voordouw@cbg-meb.nl
authors.forename: Bettie C G
authors.initials: BC
authors.lastname: Voordouw
authors.forename: Miriam C J M
authors.initials: MC
authors.lastname: Sturkenboom
authors.forename: Jeanne P
authors.initials: JP
authors.lastname: Dieleman
authors.forename: Theo
authors.initials: T
authors.lastname: Stijnen
authors.forename: Johan
authors.initials: J
authors.lastname: van der Lei
authors.forename: Bruno H C
authors.initials: BH
authors.lastname: Stricker
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D015897:Comorbidity; D019992:Databases as Topic; D005260:Female; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage*; D008297:Male; D009426:Netherlands / Q000453:epidemiology; D011014:Pneumonia / Q000453:epidemiology*; D016016:Proportional Hazards Models; D012141:Respiratory Tract Infections / Q000453:epidemiology*; D012306:Risk; D012737:Sex Factors; D014611:Vaccination / Q000706:statistics & numerical data*
chemical_list: D007252:Influenza Vaccines