title: Influenza vaccine effectiveness in households with children during the 2012-2013 season: assessments of prior vaccination and serologic susceptibility.
abstract: BACKGROUND
  There are recognized needs to identify determinants of influenza vaccine effectiveness (VE), including the effect of repeated annual vaccination.
  
  
  METHODS
  We recruited 321 households with 1426 members, including 833 children, and followed them during the 2012-2013 influenza season; specimens were collected from subjects with reported acute respiratory illnesses. We estimated the effectiveness of documented influenza vaccination in preventing laboratory-confirmed influenza, using adjusted Cox proportional hazards models. Antibody titers in a subset of subjects were determined by a hemagglutination inhibition assay to determine the subjects' preseason susceptibility to influenza.
  
  
  RESULTS
  Influenza was identified in 76 (24%) households and 111 (8%) individuals. VE point estimates indicated significant protection in adults (48%; 95% confidence interval [CI], 1%-72%), similar protection in children aged 9-17 years (49%; 95% CI, -16% to 78%), but no evidence of effectiveness in children aged <9 years (-4%; 95% CI, -110% to 49%). Lower VE was observed in those vaccinated in both the current and prior seasons, compared with those vaccinated in the current season only; susceptibility titers against type A but not type B were consistent with this observation. Residual protection from vaccination in the prior season was indicated by both VE and serologic results.
  
  
  CONCLUSIONS
  Prior vaccination appears to modify VE by both residual protection and reduced vaccine response.
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor.
authors.forename: Suzanne E
authors.initials: SE
authors.lastname: Ohmit
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor.
authors.forename: Joshua G
authors.initials: JG
authors.lastname: Petrie
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor.
authors.forename: Ryan E
authors.initials: RE
authors.lastname: Malosh
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Fry
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Thompson
authors.affiliation: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor.
authors.forename: Arnold S
authors.initials: AS
authors.lastname: Monto
mesh_terms: D000293:Adolescent; D000328:Adult; D000914:Antibodies, Viral / Q000097:blood*; D002648:Child; D005191:Family Characteristics; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology* / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines
keywords: households with children; influenza; serologic susceptibility; vaccine effectiveness