title: A cohort study of the effectiveness of influenza vaccine in older people, performed using the United Kingdom general practice research database.
abstract: BACKGROUND
  The effectiveness of influenza vaccination against hospitalization and death can only ethically be assessed in observational studies. A concern is that individuals who are vaccinated are healthier than individuals who are not vaccinated, potentially biasing estimates of effectiveness upward.
  
  
  METHODS
  We conducted a historical cohort study of individuals >64 years of age, for whom there were data available in the General Practice Research Database for 1989 to 1999 in England and Wales. Rates of admissions for acute respiratory diseases and rates of death due to respiratory disease were compared over 692,819 person-years in vaccine recipients and 1,534,280 person-years in vaccine nonrecipients.
  
  
  RESULTS
  The pooled effectiveness of vaccine against hospitalizations for acute respiratory disease was 21% (95% confidence interval [CI], 17%-26%). The rate reduction attributable to vaccination was 4.15 hospitalizations/100,000 person-weeks in the influenza season. Among vaccine recipients, no important reduction in the number of admissions to the hospital was seen outside influenza seasons. The pooled effectiveness of vaccine against deaths due to respiratory disease was 12% (95% CI, 8%-16%). A greater proportionate reduction was seen among people without medical disorders, but absolute rate reduction was higher in individuals with medical disorders, compared with individuals without such disorders (6.14 deaths due to respiratory disease/100,000 person-weeks vs. 3.12 deaths due to respiratory disease/100,000 person-weeks). Clear protection against death due to all causes was not seen.
  
  
  CONCLUSIONS
  Influenza vaccination reduces the number of hospitalizations and deaths due to respiratory disease, after correction for confounding in individuals >64 years of age who had a high risk or a low risk for influenza. For elderly people, untargeted influenza vaccination is of confirmed benefit against serious outcomes.
authors.affiliation: London School of Hygiene and Tropical Medicine, London, United Kingdom. punam.mangtani@lshtm.ac.uk
authors.forename: Punam
authors.initials: P
authors.lastname: Mangtani
authors.forename: Phillippa
authors.initials: P
authors.lastname: Cumberland
authors.forename: Cathy R
authors.initials: CR
authors.lastname: Hodgson
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Roberts
authors.forename: Felicity T
authors.initials: FT
authors.lastname: Cutts
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Hall
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D016208:Databases, Factual; D005194:Family Practice / Q000706:statistics & numerical data*; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000401:mortality / Q000517:prevention & control*; D012140:Respiratory Tract Diseases / Q000401:mortality* / Q000517:prevention & control*; D016896:Treatment Outcome; D006113:United Kingdom; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines