title: Waning vaccine protection against influenza A (H3N2) illness in children and older adults during a single season.
abstract: BACKGROUND
  Recent studies have suggested that vaccine-induced protection against influenza may decline within one season. We reanalyzed data from a study of influenza vaccine effectiveness to determine if time since vaccination was an independent predictor of influenza A (H3N2).
  
  
  METHODS
  Patients with acute respiratory illness were actively recruited during the 2007-2008 season. Respiratory swabs were tested for influenza, and vaccination dates were determined by a validated immunization registry. The association between influenza RT-PCR result and vaccination interval (days) was examined using multivariable logistic regression, adjusting for calendar time, age and other confounders.
  
  
  RESULTS
  There were 629 vaccinated participants, including 177 influenza A (H3N2) cases and 452 test negative controls. The mean (SD) interval from vaccination to illness onset was 101.7 (25.9) days for influenza cases and 93.0 (29.9) days for controls. There was a significant association between vaccination interval and influenza result in the main effects model. The adjusted odds ratio (aOR) for influenza was 1.12 (CI 1.01, 1.26) for every 14 day increase in the vaccination interval. Age modified the association between vaccination interval and influenza (p=0.005 for interaction). Influenza was associated with increasing vaccination interval in young children and older adults, but not in adolescents or non-elderly adults. Similar results were found when calendar week of vaccine receipt was assessed as the primary exposure variable.
  
  
  CONCLUSIONS
  Identification of influenza A (H3N2) was associated with increasing time since vaccination among young children and older adults during a single influenza season.
authors: Marshfield Clinic Research Foundation, 1000 North Oak Ave Marshfield, WI 54449, USA. Electronic address: belongia.edward@marshfieldclinic.org.
authors: Edward A
authors: EA
authors: Belongia
authors: Marshfield Clinic Research Foundation, 1000 North Oak Ave Marshfield, WI 54449, USA.
authors: Maria E
authors: ME
authors: Sundaram
authors: Marshfield Clinic Research Foundation, 1000 North Oak Ave Marshfield, WI 54449, USA.
authors: David L
authors: DL
authors: McClure
authors: Marshfield Clinic Research Foundation, 1000 North Oak Ave Marshfield, WI 54449, USA.
authors: Jennifer K
authors: JK
authors: Meece
authors: Influenza Division, U.S. Centers for Disease Control and Prevention, Atlanta, GA, USA; Battelle Memorial Institute, Atlanta, GA, USA.
authors: Jill
authors: J
authors: Ferdinands
authors: Marshfield Clinic Research Foundation, 1000 North Oak Ave Marshfield, WI 54449, USA.
authors: Jeffrey J
authors: JJ
authors: VanWormer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology* / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D009305:Nasopharynx / Q000821:virology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Immunity; Influenza; Influenza vaccine; Vaccine effectiveness