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Seasonal Incidence of Symptomatic Influenza in the United States
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    The seasonal incidence of influenza is often approximated as 5%–20%.


    We used 2 methods to estimate the seasonal incidence of symptomatic influenza in the United States. First, we made a statistical estimate extrapolated from influenza-associated hospitalization rates for 2010–2011 to 2015–2016, collected as part of national surveillance, covering approximately 9% of the United States, and including the existing mix of vaccinated and unvaccinated persons. Second, we performed a literature search and meta-analysis of published manuscripts that followed cohorts of subjects during 1996–2016 to detect laboratory-confirmed symptomatic influenza among unvaccinated persons; we adjusted this result to the US median vaccination coverage and effectiveness during 2010–2016.


    The statistical estimate of influenza incidence among all ages ranged from 3.0%–11.3% among seasons, with median values of 8.3% (95% confidence interval [CI], 7.3%–9.7%) for all ages, 9.3% (95% CI, 8.2%–11.1%) for children <18 years, and 8.9% (95% CI, 8.2%–9.9%) for adults 18–64 years. Corresponding values for the meta-analysis were 7.1% (95% CI, 6.1%–8.1%) for all ages, 8.7% (95% CI, 6.6%–10.5%) for children, and 5.1% (95% CI, 3.6%–6.6%) for adults.


    The 2 approaches produced comparable results for children and persons of all ages. The statistical estimates are more versatile and permit estimation of season-to-season variation. During 2010–2016, the incidence of symptomatic influenza among vaccinated and unvaccinated US residents, including both medically attended and nonattended infections, was approximately 8% and varied from 3% to 11% among seasons.

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