title: Increase in reported adverse events following seasonal influenza vaccination among the French armed forces, 2008-2009: possible role of stimulated reporting and background cases of influenza-like infection.
abstract: OBJECTIVE
  In September 2009, an increase in seasonal influenza vaccine adverse events (VAE), compared with reports for previous years, was detected among the French armed forces in the setting of an extended immunization campaign. This work presents the results of this investigation.
  
  
  METHODS
  VAE were surveyed among all French military personnel from 2008 to 2009 by Epidemiological Departments of the French Military Health Service. For each case, a notification form was completed, providing patient and clinical information.
  
  
  METHODS
  Case definitions were derived from the French drug vigilance guidelines. Three types of VAE were considered: non-serious, serious and unexpected. Incidence rates were calculated by relating VAE to the number of vaccine doses injected.
  
  
  RESULTS
  Forty-seven seasonal influenza VAE were reported in continental France: 18 in 2008 and 29 in 2009. The annual reporting rate was higher in 2009 (31.6 vs 16.6 VAE per 100,000 injections, respectively). The highest monthly incidence was observed in September 2009 (60.8 events per 100,000 injections). Two other peaks were observed in February 2008 and March 2009. The incidence in September 2009 was not significantly different from the incidences in February 2008 and March 2009. It was observed that incidence peaks occurred during influenza epidemic periods. One serious neurological VAE was observed.
  
  
  CONCLUSIONS
  The increase in seasonal influenza VAE in late 2009 mainly involved non-serious events, and could reflect stimulated reporting in the context of the A(H1N1)pdm09 pandemic. VAE reporting rates were highest during influenza epidemic periods, which could be explained by VAE being wrongly attributed to the vaccine when symptoms could reflect coincident background cases of viral infection.
authors.affiliation: Centre d'épidémiologie et de santé publique des armées, Hôpital d'instruction des armées Bégin, Ilot Bégin, 69 avenue de Paris, 94160 Saint Mandé, France. aurelie_marie@hotmail.fr
authors.forename: A
authors.initials: A
authors.lastname: Mayet
authors.forename: P
authors.initials: P
authors.lastname: Nivoix
authors.forename: R
authors.initials: R
authors.lastname: Haus-Cheymol
authors.forename: F
authors.initials: F
authors.lastname: De Laval
authors.forename: C
authors.initials: C
authors.lastname: Verret
authors.forename: S
authors.initials: S
authors.lastname: Duron
authors.forename: N
authors.initials: N
authors.lastname: Faure
authors.forename: M
authors.initials: M
authors.lastname: Piarroux
authors.forename: C
authors.initials: C
authors.lastname: Decam
authors.forename: H
authors.initials: H
authors.lastname: Chaudet
authors.forename: J-B
authors.initials: JB
authors.lastname: Meynard
authors.forename: X
authors.initials: X
authors.lastname: Deparis
authors.forename: R
authors.initials: R
authors.lastname: Migliani
mesh_terms: D000293:Adolescent; D000328:Adult; D064420:Drug-Related Side Effects and Adverse Reactions / Q000453:epidemiology*; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D008889:Military Personnel / Q000706:statistics & numerical data*; D012621:Seasons; D014611:Vaccination; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines