Fig. 2
From: Detecting signals of seasonal influenza severity through age dynamics
Influenza age dynamics differ from overall epidemic dynamics. a Medically attended outpatient ILI visits per 100,000 for the 2001–02 through 2008–09 flu seasons, adjusted for increasing surveillance data coverage and ILI care-seeking behavior, are displayed. The national early warning and retrospective classification periods are overlaid in green and black, respectively. b The normalized relative risk of adult ILI to child ILI rates (ρ s (t)), a proxy of age-specific disease burden, follows a regular seasonal pattern during the U.S. Thanksgiving and winter holiday periods, and diverges during the typical epidemic growth periods of January and February (around weeks 2–7)