Seasonal Incidence of Symptomatic Influenza in the United States

• Published in: Clinical infectious diseases Vol. 66; no. 10; pp. 1511 - 1518
• Main Authors: Tokars, Jerome I, Olsen, Sonja J, Reed, Carrie
• Format: Journal Article
• Language: English
• Published: United States 02.05.2018
• Subjects: Adolescent; Adult; Aged; Centers for Disease Control and Prevention, U.S; Child; Child, Preschool; Female; Humans; Incidence; Infant; Influenza, Human - epidemiology; Male; Middle Aged; Seasons; United States - epidemiology; Young Adult; United States
• ISSN: 1058-4838; 1537-6591; 1537-6591
• DOI: 10.1093/cid/cix1060

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.