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Some data suggest that children are important vectors in the spread of seasonal influenza. In a cluster-randomized double-blind study, investigators examined whether immunizing children (age range, 3–15 years) against influenza protects the whole community. This study was conducted in Hutterite colonies (religious communities of <120 people) in rural Canada during the 2008–2009 influenza season.
Children in 22 colonies received influenza vaccine, and children in 24 colonies received hepatitis A vaccine (control). The children and their contacts in the community were assessed for illness twice weekly and tested by polymerase chain reaction (PCR) if symptoms developed. Six influenza-vaccinated and 13 hepatitis-vaccinated colonies experienced outbreaks. Overall, 119 cases of influenza were confirmed by PCR: 39 of 1271 unvaccinated individuals in the flu-vaccinated communities and 80 of 1055 individuals in the hepatitis A–vaccinated communities (3.1% vs. 7.6%). Immunization of children conferred significant protection against influenza among unvaccinated community members (61%).
Loeb M et al. Effect of influenza vaccination of children on infection rates in Hutterite communities: A randomized trial. JAMA 2010 Mar 10; 303:943.
Comment
This unique study provides the most clear-cut evidence to date of the importance of children in the spread of influenza. Immunization of children not only protected children but conferred a large protective effect on the entire community. When vaccine shortages occur, vaccination of children, in addition to other high-risk groups, should be a high priority.