Effectiveness of influenza vaccination of schoolchildren in the city of São Paulo, Brazil, 2009

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 1,742 schoolchildren as well as 5,406 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 six months in order 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). CONCLUSION Vaccination of schoolchildren significantly protected them and their household contacts against seasonal influenza. This article is protected by copyright. All rights reserved.