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U-shaped and W-shaped combined influenza and pneumonia mortality, by age at death, per 100,000 persons in each age group, US, 1911 to 1918. Influenza/pneumonia-specific death rates are plotted for the years before the pandemic, ie, 1911 to 1917 (blue line), and for the pandemic year 1918 (red line) (7, 66, 67).
