title: Impact of repeated vaccination on vaccine effectiveness against influenza A(H3N2) and B during 8 seasons.
abstract: BACKGROUND
  Recent studies suggest that influenza vaccination in the previous season may influence the effectiveness of current-season vaccination, but this has not been assessed in a single population over multiple years.
  
  
  METHODS
  Patients presenting with acute respiratory illness were prospectively enrolled during the 2004-2005 through 2012-2013 influenza seasons. Respiratory swabs were tested for influenza and vaccination dates obtained from a validated registry. Vaccination status was determined for the current, previous, and prior 5 seasons. Vaccine effectiveness (VE) was calculated for participants aged ≥9 years using logistic regression models with an interaction term for vaccination history.
  
  
  RESULTS
  There were 7315 enrollments during 8 seasons; 1056 (14%) and 650 (9%) were positive for influenza A(H3N2) and B, respectively. Vaccination during current only, previous only, or both seasons yielded similar protection against H3N2 (adjusted VE range, 31%-36%) and B (52%-66%). In the analysis using 5 years of historical vaccination data, current season VE against H3N2 was significantly higher among vaccinated individuals with no prior vaccination history (65%; 95% confidence interval [CI], 36%-80%) compared with vaccinated individuals with a frequent vaccination history (24%; 95% CI, 3%-41%; P = .01). VE against B was 75% (95% CI, 50%-87%) and 48% (95% CI, 29%-62%), respectively (P = .05). Similar findings were observed when analysis was restricted to adults 18-49 years.
  
  
  CONCLUSIONS
  Current- and previous-season vaccination generated similar levels of protection, and vaccine-induced protection was greatest for individuals not vaccinated during the prior 5 years. Additional studies are needed to understand the long-term effects of annual vaccination.
authors.affiliation: Center for Clinical Epidemiology and Population Health, Marshfield Clinic Research Foundation, Wisconsin.
authors.forename: Huong Q
authors.initials: HQ
authors.lastname: McLean
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Thompson
authors.affiliation: Center for Clinical Epidemiology and Population Health, Marshfield Clinic Research Foundation, Wisconsin.
authors.forename: Maria E
authors.initials: ME
authors.lastname: Sundaram
authors.affiliation: Integrated Research and Development Laboratory, Marshfield Clinic Research Foundation.
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Meece
authors.affiliation: Center for Clinical Epidemiology and Population Health, Marshfield Clinic Research Foundation, Wisconsin.
authors.forename: David L
authors.initials: DL
authors.lastname: McClure
authors.affiliation: Department of Pathobiological Sciences, University of Wisconsin School of Veterinary Medicine, Wisconsin National Primate Research Center, Madison.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Friedrich
authors.affiliation: Center for Clinical Epidemiology and Population Health, Marshfield Clinic Research Foundation, Wisconsin.
authors.forename: Edward A
authors.initials: EA
authors.lastname: Belongia
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D015897:Comorbidity; D005260:Female; D006801:Humans; D007117:Immunization, Secondary; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology*; D009981:Influenza B virus / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D012307:Risk Factors; D012621:Seasons; D014611:Vaccination; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: influenza; vaccine effectiveness