title: Safety of trivalent inactivated influenza vaccine in children 6 to 23 months old.
abstract: BACKGROUND
  Beginning with the winter season of 2004-2005, influenza vaccination has been recommended for all children 6 to 23 months old in the United States. However, its safety in young children has not been adequately studied in large populations.
  
  
  OBJECTIVE
  To screen for medically attended events in the clinic, emergency department, or hospital after administration of trivalent inactivated influenza vaccine in children 6 to 23 months old.
  
  
  METHODS
  Retrospective cohort using self-control analysis, with chart review of significant medically attended events at 8 managed care organizations in the United States that comprise the Vaccine Safety Datalink. Participants were all children in the Vaccine Safety Datalink cohort 6 to 23 months old who received trivalent inactivated influenza vaccine between January 1, 1991, and May 31, 2003 (45,356 children with 69,359 vaccinations).
  
  
  METHODS
  Any medically attended event significantly associated with trivalent inactivated influenza vaccine in risk windows 0 to 3 days, 1 to 14 days (primary analysis), 1 to 42 days, or 15 to 42 days after vaccination, compared with 2 control periods, one before vaccination and the second after the risk window. All individual ICD-9 codes as well as predefined aggregate codes were examined.
  
  
  RESULTS
  Before chart review, only 1 diagnosis, gastritis/duodenitis, was more likely to occur in the 14 days after trivalent inactivated influenza vaccine (matched odds ratio [OR], 5.50; 95% confidence interval [CI], 1.22-24.81 for control period 1, and matched OR, 4.33; 95% CI, 1.23-15.21 for control period 2). Thirteen medically attended events were less likely to occur after trivalent inactivated influenza vaccine, including acute upper respiratory tract infection, asthma, bronchiolitis, and otitis media. After chart review, gastritis/duodenitis was not significantly associated with trivalent inactivated influenza vaccine (matched OR, 4.00; 95% CI, 0.85-18.84 for control period 1; matched OR, 3.34; 95% CI, 0.92-12.11 for control period 2).
  
  
  CONCLUSIONS
  In the largest population-based study to date of the safety of trivalent inactivated influenza vaccine in young children, there were very few medically attended events, none of which were serious, significantly associated with the vaccine. This study provides additional evidence supporting the safety of universally immunizing all children 6 to 23 months old with influenza vaccine.
authors.affiliation: Clinical Research Unit, Kaiser Permanente Colorado, Denver, CO 80237-8066, USA. simon.hambidge@dhha.org
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Hambidge
authors.forename: Jason M
authors.initials: JM
authors.lastname: Glanz
authors.forename: Eric K
authors.initials: EK
authors.lastname: France
authors.forename: David
authors.initials: D
authors.lastname: McClure
authors.forename: Stanley
authors.initials: S
authors.lastname: Xu
authors.forename: Kristi
authors.initials: K
authors.lastname: Yamasaki
authors.forename: Lisa
authors.initials: L
authors.lastname: Jackson
authors.forename: John P
authors.initials: JP
authors.lastname: Mullooly
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Zangwill
authors.forename: S Michael
authors.initials: SM
authors.lastname: Marcy
authors.forename: Steven B
authors.initials: SB
authors.lastname: Black
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Lewis
authors.forename: Henry R
authors.initials: HR
authors.lastname: Shinefield
authors.forename: Edward
authors.initials: E
authors.lastname: Belongia
authors.forename: James
authors.initials: J
authors.lastname: Nordin
authors.forename: Robert T
authors.initials: RT
authors.lastname: Chen
authors.forename: David K
authors.initials: DK
authors.lastname: Shay
authors.forename: Robert L
authors.initials: RL
authors.lastname: Davis
authors.forename: Frank
authors.initials: F
authors.lastname: DeStefano
mesh_terms: D015331:Cohort Studies; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000009:adverse effects*; D011159:Population Surveillance; D012044:Regression Analysis; D012189:Retrospective Studies; D012306:Risk; D014481:United States; D015164:Vaccines, Inactivated
chemical_list: D007252:Influenza Vaccines; D015164:Vaccines, Inactivated