title: The population impact of a large school-based influenza vaccination campaign.
abstract: BACKGROUND
  The optimal vaccination strategy to mitigate the impact of influenza epidemics is unclear. In 2005, a countywide school-based influenza vaccination campaign was launched in Knox County, Tennessee (population 385,899). Approximately 41% and 48% of eligible county children aged 5-17 years were immunized with live attenuated influenza vaccine before the 2005-2006 and 2006-2007 influenza seasons, respectively. We sought to determine the population impact of this campaign.
  
  
  METHODS
  Laboratory-confirmed influenza data defined influenza seasons. We calculated the incidence of medically attended acute respiratory illness attributable to influenza in Knox and Knox-surrounding counties (concurrent controls) during consecutive seasons (5 precampaign and 2 campaign seasons) using negative binomial regression and rate difference methods. Age-stratified analyses compared the incidence of emergency department (ED) visits and hospitalizations attributable to influenza.
  
  
  RESULTS
  During precampaign seasons, estimated ED visit rates attributable to influenza were 12.39 (95% CI: 10.34-14.44) per 1000 Knox children aged 5-17 years and similar in Knox-surrounding counties. During the campaign seasons, annual Knox influenza-associated ED visit rates declined relative to rates in Knox-surrounding counties: rate ratios 0.55 (95% CI: 0.27-0.83) and 0.70 (95% CI: 0.56-0.84) for the first and second campaign seasons, respectively. Overall, there were about 35% or 4.86 per 1000 fewer influenza-associated ED visits among Knox County children aged 5-17 years attributable to the campaign. No significant declines in Knox compared to surrounding counties were detected for influenza associated ED visits in children aged <5 years, all adults combined or selected adult age subgroups, although power for these analyses was limited. Alternate rate-difference analyses yielded consistent results.
  
  
  CONCLUSIONS
  Vaccination of approximately 45% of Knox school-aged children with influenza vaccine was associated with a 35% annual reduction (4.86 per 1000) in ED visit rates attributable to influenza. Higher vaccination coverage and/or larger studies would be needed to determine whether similar interventions have indirect benefits in other age groups.
authors.affiliation: Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America. carlos.grijalva@vanderbilt.edu
authors.forename: Carlos G
authors.initials: CG
authors.lastname: Grijalva
authors.forename: Yuwei
authors.initials: Y
authors.lastname: Zhu
authors.forename: Lone
authors.initials: L
authors.lastname: Simonsen
authors.forename: Edward
authors.initials: E
authors.lastname: Mitchel
authors.forename: Marie R
authors.initials: MR
authors.lastname: Griffin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D017589:Immunization Programs / Q000458:organization & administration / Q000706:statistics & numerical data*; D015994:Incidence; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000150:complications / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D015397:Program Evaluation / Q000706:statistics & numerical data; D012120:Respiration Disorders / Q000453:epidemiology / Q000209:etiology; D012574:Schools; D012621:Seasons; D013714:Tennessee / Q000453:epidemiology; D014611:Vaccination / Q000379:methods*; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines