title: Effectiveness of influenza vaccine in children in day-care centers of Sapporo.
abstract: BACKGROUND
  We conducted a retrospective cohort study for evaluating the effectiveness of the trivalent inactivated influenza vaccine (TIV) among children aged 0-6 years in the 2011-2012 season in Sapporo City, Japan, because of scarce evidence.
  
  
  METHODS
  From 10 day-care centers in Sapporo City, Japan, 629 parents participated in the study. Each parent of the subjects described whether a subject received TIV once or twice in the 2011-2012 season, as well as the exact dates of receiving TIV from records in a maternal and child health handbook marked by a pediatrician. The incidence of influenza was defined as being affected with influenza as diagnosed by a pediatrician. Cox's proportional model was used for calculating a hazard ratio (HR) and its 95% confidence interval (95%CI) of TIV on an influenza incidence.
  
  
  RESULTS
  After adjusting potential confounding variables, such as the day-care center, presence of comorbidity, size of household, number of siblings, and number of smokers in the home in addition to the age and sex of the child, HR was significantly reduced in the subjects aged 1 year (HR = 0.22, 95%CI 0.09-0.54) as well as in the total subjects (HR = 0.72, 95%CI 0.52-0.99). Consequently, the effectiveness of TIV was calculated as 78% for the subjects aged 1 year and 28% for the total subjects.
  
  
  CONCLUSIONS
  Our study suggests that TIV is effective, especially in subjects aged 1 year. Further studies are necessary in different seasons, places, and populations to clarify the effectiveness of the influenza vaccine in children.
authors.affiliation: Department of Public Health, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Mori
authors.forename: Junko
authors.initials: J
authors.lastname: Hasegawa
authors.forename: Satoko
authors.initials: S
authors.lastname: Showa
authors.forename: Aiko
authors.initials: A
authors.lastname: Matsushima
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Ohnishi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tsutsumi
mesh_terms: D002648:Child; D002656:Child Day Care Centers / Q000706:statistics & numerical data*; D002675:Child, Preschool; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D009980:Influenza A virus / Q000276:immunology*; D007252:Influenza Vaccines / Q000494:pharmacology*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D007564:Japan / Q000453:epidemiology; D011379:Prognosis; D012189:Retrospective Studies; D014505:Urban Population
chemical_list: D007252:Influenza Vaccines
keywords: children; effectiveness; influenza vaccine; retrospective cohort studies