Influenza in older adults: Impact of vaccination of school children
Introduction
Although trivalent inactivated influenza vaccination (TIV) is recommended for all persons aged ≥50 years, recent reports have questioned its effectiveness for the prevention of influenza-associated morbidity and mortality in older adults [1], [2], [3]. This concern has increased interest in evaluating indirect effects of vaccinating children upon disease burden in older adults. To date, support for indirect or “herd” effects from immunization of school children is based on a few provocative reports, none of which included laboratory-confirmed influenza as an endpoint [4], [5], [6]. In a study conducted during the 1968 influenza pandemic, outpatient visits for acute respiratory illness (ARI) were reduced in all age groups in the community where school children received influenza vaccine as compared to another community where children remained unvaccinated [4]. Universal influenza vaccination of school children in Japan was also associated with a striking reduction in seasonal pneumonia and influenza mortality in the older population and young children [5], [6].
To further investigate the role of indirect protection of the older population through immunization of school children, we performed active, prospective influenza surveillance in adults ≥50 years hospitalized with respiratory symptoms or non-localizing fever in Knox County, where a school-based influenza immunization campaign was conducted, and in Davidson County, where there was no such program. The goal was to compare the burden of influenza-associated hospitalizations in adults aged ≥50 years in the two counties, one with and one without a school-based influenza vaccination program.
Section snippets
Study design
To compare adult hospitalization rates for laboratory-confirmed influenza in two geographically distinct Tennessee counties, we enrolled adults ≥50 years hospitalized with respiratory symptoms or non-localizing fever at two hospitals in each county during the influenza season. Recruitment occurred from November 2006 through April 2007 beginning 2 days per week. Once two cases of influenza were identified for 2 consecutive weeks in the hospital laboratories in each county, surveillance increased
Results
Surveillance in both counties began the first full week in November 2006 and continued through April 30, 2007. However, all influenza-positive samples were identified during the 18 weeks from December 10, 2006 through April 14, 2007, defined as the influenza season. The timing of the season was similar in both counties. All analyses included persons admitted during the 18-week influenza season.
Discussion
Due to the disproportionate morbidity and mortality of influenza for persons ≥65 years [11], [12], [13], [14], [15], [16], [17], United States public health officials have recommended routine annual influenza vaccination to these individuals for many years. Recently all adults ≥50 years were also recommended to receive yearly influenza vaccination [18]. However, in the past several years there has been increasing concern over suboptimal efficacy in older adults. Therefore, alternative
Acknowledgements
We would like to thank Dr. William Schaffner for his review and recommendations regarding this manuscript.
Financial support: Funding for this study was through multiple sources: an investigator initiated grant from MedImmune (Marie R Griffin, PI) supported the Knox County surveillance activities and the data analysis and the VTEU (N01 AI25462) (Kathryn M. Edwards site PI) supported the adult influenza surveillance activities in Davidson County. Dr. Talbot received salary support and career
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