title: Effectiveness of influenza vaccination of schoolchildren in the city of São Paulo, Brazil, 2009.
abstract: BACKGROUND
  Children play an important role in maintaining the transmission of influenza. Evidence suggests that vaccination of school-age children can reduce transmission to unvaccinated household contacts. We evaluated the direct and indirect effectiveness of the 2009 inactivated seasonal influenza vaccine in vaccinated schoolchildren and their unvaccinated household contacts.
  
  
  METHODS
  This was a double-blind cluster randomized trial involving 10 schools and 1742 schoolchildren as well as 5406 household contacts. The schools were randomly assigned to receive the influenza vaccine or the control vaccine. After vaccination, the schoolchildren and household contacts were followed for 6 months to identify cases of acute respiratory infection (ARI). Reverse-transcriptase polymerase chain reaction was performed for the diagnosis of influenza.
  
  
  RESULTS
  A total of 632 ARI cases were detected. Of those, 103 tested positive for influenza virus (influenza virus A[H1N1]pdm09 virus in 55 and seasonal influenza viruses in 48). The effectiveness of the vaccine in protecting against seasonal influenza virus infection was 65·0% for the household contacts (95% CI, 19·6-84·3) and 65·0% for the schoolchildren (95% CI, 20·9-84·5).
  
  
  CONCLUSIONS
  Vaccination of schoolchildren significantly protected them and their household contacts against seasonal influenza.
authors.affiliation: Butantan Institute, São Paulo, Brazil.
authors.forename: Vera L
authors.initials: VL
authors.lastname: Gattás
authors.affiliation: School of Public Health, University of São Paulo, São Paulo, Brazil.
authors.forename: Maria Regina A
authors.initials: MRA
authors.lastname: Cardoso
authors.affiliation: Butantan Institute, São Paulo, Brazil.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Mondini
authors.affiliation: Institute of Tropical Medicine, University of São Paulo, São Paulo, Brazil.
authors.forename: Clarisse M
authors.initials: CM
authors.lastname: Machado
authors.affiliation: Institute of Tropical Medicine, University of São Paulo, São Paulo, Brazil.
authors.forename: Expedito J A
authors.initials: EJA
authors.lastname: Luna
keywords: Effectiveness; influenza; intervention study; school-age children; vaccination