title: Potential of the test-negative design for measuring influenza vaccine effectiveness: a systematic review.
abstract: BACKGROUND
  The test-negative design is a variant of the case-control study being increasingly used to study influenza vaccine effectiveness (VE). In these studies, patients with influenza-like illness are tested for influenza. Vaccine coverage is compared between those testing positive versus those testing negative to estimate VE.
  
  
  OBJECTIVE
  We reviewed features in the design, analysis and reporting of 85 published test-negative studies.
  
  
  METHODS
  Studies were identified from PubMed, reference lists and email updates. Study eligibility: All studies using the test-negative design reporting end-of-season estimates were included.
  
  
  METHODS
  Design features that may affect the validity and comparability of reported estimates were reviewed, including setting, study period, source population, case definition, exposure and outcome ascertainment and statistical model.
  
  
  RESULTS
  There was considerable variation in the analytic approach, with 68 unique statistical models identified among the studies.
  
  
  CONCLUSIONS
  Harmonization of analytic approaches may improve the potential for pooling VE estimates.
authors.affiliation: WHO Collaborating Centre for Reference and Research on Influenza, Peter Doherty Institute for Infection and Immunity , 792 Elizabeth St, Melbourne VIC 3000 , Australia.
authors.forename: Sheena G
authors.initials: SG
authors.lastname: Sullivan
authors.forename: Shuo
authors.initials: S
authors.lastname: Feng
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
mesh_terms: D000293:Adolescent; D000328:Adult; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: case–control; influenza; public health; test-negative study; vaccine effectiveness