title: Assessment of influenza vaccine effectiveness in a sentinel surveillance network 2010-13, United States.
abstract: BACKGROUND
  Influenza vaccines are now widely used to reduce the burden of annual epidemics of influenza virus infections. Influenza vaccine effectiveness (VE) is monitored annually to determine VE against each season's circulating influenza strains in different groups such as children, adults and the elderly. Few prospective surveillance programs are available to evaluate influenza VE against medically attended illness for patients of all ages in the United States.
  
  
  METHODS
  We conducted surveillance of patients with acute respiratory illnesses in 101 clinics across the US during three consecutive influenza seasons. We analyzed laboratory testing results for influenza virus, self-reported vaccine history, and patient characteristics, defining cases as patients who tested positive for influenza virus and controls as patients who tested negative for influenza virus. Comparison of influenza vaccination coverage among cases versus controls, adjusted for potential confounders, was used to estimate VE as one minus the adjusted odds ratio multiplied by 100%.
  
  
  RESULTS
  We included 10,650 patients during three influenza seasons from August 2010 through December 2013, and estimated influenza VE in children 6m-5y of age (58%; 95% CI: 49%-66%), children 6-17y (45%; 95% CI: 34%-53%), adults 18-49y (36%; 95% CI: 24%, 46%), and adults ≥50y (34%, 95% CI: 13%, 51%). VE was higher against influenza A(H1N1) compared to A(H3N2) and B.
  
  
  CONCLUSIONS
  Our estimates of moderate influenza VE confirm the important role of vaccination in protecting against medically attended influenza virus infection.
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region.
authors.forename: Shuo
authors.initials: S
authors.lastname: Feng
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, United States.
authors.forename: Lyn
authors.initials: L
authors.lastname: Finelli
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, United States.
authors.forename: Andrea
authors.initials: A
authors.lastname: Steffens
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, United States. Electronic address: AFowlkes@cdc.gov.
authors.forename: Ashley
authors.initials: A
authors.lastname: Fowlkes
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D018571:Sentinel Surveillance; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Influenza vaccine; Influenza-like illness; Respiratory infection; Vaccine efficacy