title: How and why researchers use the number needed to vaccinate to inform decision making--a systematic review.
abstract: BACKGROUND
  The number needed to vaccinate (NNV) is a measure that has been widely used in the scientific literature to draw conclusions about the usefulness and cost-effectiveness of various immunization programmes. The main objective of this review is to examine how and why the NNV has been used and reported in the published literature.
  
  
  METHODS
  Electronic databases were searched and records were screened against the eligibility criteria by two independent authors. We included papers that reported and interpreted NNV.
  
  
  RESULTS
  We identified 27 studies, the designs including observational studies, economic analyses, systematic reviews, and commentaries. The NNV has been used in the literature to describe three main themes: potential benefits of vaccination programmes, cost-effectiveness, and economic analyses, and modelling studies to compare different vaccination strategies.
  
  
  CONCLUSIONS
  NNV has been used in a wide variety of ways in the literature, yet there are no defined thresholds for what is a favourable NNV. Furthermore, the generalizability of the NNV is usually limited. Further work is required to determine the most appropriate use of this measure.
authors.affiliation: Public Health Ontario, 480 University Avenue, Suite 300, Toronto, ON, Canada M5G 1V2. Electronic address: ahmed_basim81@yahoo.com.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Hashim
authors.affiliation: Public Health Ontario, 480 University Avenue, Suite 300, Toronto, ON, Canada M5G 1V2. Electronic address: vica.dang@oahpp.ca.
authors.forename: Vica
authors.initials: V
authors.lastname: Dang
authors.affiliation: Public Health Ontario, 480 University Avenue, Suite 300, Toronto, ON, Canada M5G 1V2; Dalla Lana School of Public Health, University of Toronto , 155 College St, Toronto, ON, Canada M5T 3M7. Electronic address: shelly.bolotin@oahpp.ca.
authors.forename: Shelly
authors.initials: S
authors.lastname: Bolotin
authors.affiliation: Public Health Ontario, 480 University Avenue, Suite 300, Toronto, ON, Canada M5G 1V2; Dalla Lana School of Public Health, University of Toronto , 155 College St, Toronto, ON, Canada M5T 3M7; Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto , Medical Sciences Building, 1 King's College Circle, Toronto, ON, Canada M5S 1A8. Electronic address: natasha.crowcroft@oahpp.ca.
authors.forename: Natasha S
authors.initials: NS
authors.lastname: Crowcroft
mesh_terms: D001424:Bacterial Infections / Q000191:economics / Q000276:immunology / Q000517:prevention & control; D001428:Bacterial Vaccines / Q000008:administration & dosage / Q000191:economics*; D003362:Cost-Benefit Analysis; D016206:Databases, Bibliographic; D003657:Decision Making; D006301:Health Services Needs and Demand / Q000191:economics / Q000706:statistics & numerical data*; D006801:Humans; D015233:Models, Statistical; D012107:Research Design / Q000706:statistics & numerical data*; D014611:Vaccination / Q000191:economics / Q000706:statistics & numerical data*; D014765:Viral Vaccines / Q000008:administration & dosage / Q000191:economics*; D014777:Virus Diseases / Q000191:economics / Q000276:immunology / Q000517:prevention & control
chemical_list: D001428:Bacterial Vaccines; D014765:Viral Vaccines
keywords: Benefits of vaccination; Cost-effectiveness; Immunization; Mathematicalmodelling; Number needed to treat; Number needed to vaccinate