Seasonal

influenza is an important cause ofvisits to the emergency department amongchildren during winter months, and its control and prevention rely on annual vaccina-tion.1−4 In the United States, the Advisory Com-mittee on Immunization Practices is responsible for guiding immunization practices, and it revises its recommendations annually. Until the 2004/2005 influenza season, vaccination was tar-geted to primarily older individuals and those with certain medical conditions.5 On the basis of evidence that young children are at elevated risk for admission to hospital because of influenza-related complications, the recommendations were expanded for the 2004/2005 season to include healthy children aged 6−23 months.6 Starting in the 2006/2007 season, the recom-mendations of the Advisory Committee on Immunization Practices regarding influenza vac-cination were expanded again to include healthy children aged 24–59 months, a shift that added 10.6 million children to the target group.7 For the 2008/2009 season, recommendations were fur-ther expanded to include all persons 6 months to 18 years old,8 and for the 2010/2011 season, the influenza vaccine was advised for all individuals over 6 months of age.9 In Canada, the National Advisory Committee on Immunization is the federal organization responsible for guiding the use of vaccines. Until the 2006/2007 season, the recommendations of this committee for the use of seasonal influenza vaccines were harmonized with those of its US counterpart. However, it was not until the Effect of expanded US recommendations for seasonal influenza vaccination: comparison of two pediatric emergency departments in the United States and Canad