1. Trivalent influenza vaccine (TIV) was found to be 85.5% effective in children aged 6 months to 2 years.
2. TIV was more effective against influenza A than influenza B among children aged 6 months to 5 years.
Evidence Rating Level: 2 (Good)
Study Rundown: Annual influenza vaccination is the mainstay of public health efforts to reduce the burden of seasonal influenza, a significant contributor to acute respiratory infections among pediatric patients worldwide. Although national recommendations vary, vaccination of pediatric patients is viewed as a priority. The U.S. and other nations recommend trivalent influenza vaccine (TIV) for children aged 6 months and older or live-attenuated influenza vaccine (LAIV), administered via nasal spray, for children aged 2 years and older. The role of influenza vaccination in children younger than age 2 is controversial, however, due to the lack of available data on TIV effectiveness in this age category. This study evaluated TIV effectiveness in children aged 6 months to 5 years between 2008 and 2012. Results indicate that children aged 6 months to 5 years who were vaccinated with TIV were significantly less likely to present to a hospital with influenza when compared with unvaccinated children, supporting current vaccination recommendations. This study is particularly strong because it followed patients across four influenza seasons, but is limited by low population vaccine uptake, particularly during the 2010 season.
In-Depth [prospective cohort study]: This study evaluated TIV effectiveness in children aged 6 months to 5 years between 2008 and 2012 in Western Australia. Children presenting with an influenza-like illness to a major pediatric teaching hospital were enrolled in the study and evaluated for the presence of the influenza virus by PCR of nasopharyngeal swabs. Children testing positive for influenza were identified as cases (N=389), while children testing negative were identified as controls (N=1514). Vaccine effectiveness, adjusting for age, gender, comorbidities, and other associated factors, was calculated to be 65.8% among all participants (95% CI: 32.1 to 82.8%), and 85.5% in children under 2 years of age (95% CI: 34.7 to 96.8%). When calculated by influenza subtype, TIV effectiveness was found to be higher for influenza A (79.6%, 95% CI: 41.6 to 92.9%) than for influenza B (47.8%, 95% CI: -12.4 to 75.8%). Among partially vaccinated children (ie. those receiving only one of two recommended doses), vaccine effectiveness was found to be 81.5% (95% CI: 54.7 to 92.4%).
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