title: Inducing Herd Immunity against Seasonal Influenza in Long-Term Care Facilities through Employee Vaccination Coverage: A Transmission Dynamics Model.
abstract: BACKGROUND
  Vaccinating healthcare workers (HCWs) in long-term care facilities (LTCFs) may effectively induce herd immunity and protect residents against influenza-related morbidity and mortality. We used influenza surveillance data from all LTCFs in New Mexico to validate a transmission dynamics model developed to investigate herd immunity induction.
  
  
  METHODS
  We adjusted a previously published transmission dynamics model and used surveillance data from an active system among 76 LTCFs in New Mexico during 2006-2007 for model validation. We used a deterministic compartmental model with a stochastic component for transmission between residents and HCWs in each facility in order to simulate the random variation expected in such populations.
  
  
  RESULTS
  When outbreaks were defined as a dichotomous variable, our model predicted that herd immunity could be induced. When defined as an attack rate, the model demonstrated a curvilinear trend, but insufficiently strong to induce herd immunity. The model was sensitive to changes in the contact parameter β but was robust to changes in the visitor contact probability.
  
  
  CONCLUSIONS
  These results further elucidate previous studies' findings that herd immunity may not be induced by vaccinating HCWs in LTCFs; however, increased influenza vaccination coverage among HCWs reduces the probability of influenza infection among residents.
authors.affiliation: Department of Biostatistics and Epidemiology, College of Public Health, University of Oklahoma Health Sciences Center, 801 NE 13th Street, CHB 323, Oklahoma City, OK 73104, USA.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Wendelboe
authors.affiliation: Department of Biostatistics and Epidemiology, College of Public Health, University of Oklahoma Health Sciences Center, 801 NE 13th Street, CHB 323, Oklahoma City, OK 73104, USA.
authors.forename: Carl
authors.initials: C
authors.lastname: Grafe
authors.affiliation: Department of Biostatistics and Epidemiology, College of Public Health, University of Oklahoma Health Sciences Center, 801 NE 13th Street, CHB 323, Oklahoma City, OK 73104, USA.
authors.forename: Micah
authors.initials: M
authors.lastname: McCumber
authors.affiliation: Department of Biostatistics and Epidemiology, College of Public Health, University of Oklahoma Health Sciences Center, 801 NE 13th Street, CHB 323, Oklahoma City, OK 73104, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Anderson
mesh_terms: D019295:Computational Biology; D004196:Disease Outbreaks / Q000517:prevention & control / Q000706:statistics & numerical data; D062665:Epidemiological Monitoring; D006282:Health Personnel; D006801:Humans; D032521:Immunity, Herd; D017757:Infectious Disease Transmission, Professional-to-Patient / Q000517:prevention & control; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology* / Q000635:transmission; D016014:Linear Models; D008134:Long-Term Care; D018448:Models, Immunological; D015233:Models, Statistical; D009516:New Mexico / Q000453:epidemiology; D012112:Residential Facilities; D012621:Seasons; D013269:Stochastic Processes; D014611:Vaccination