Combined influenza and pneumonia mortality, United States, 1911-1918

"U-" and "W-" shaped combined influenza and pneumonia mortality, by age at death, per 100,000 persons in each age group, United States, 1911-1918. Influenza- and pneumonia-specific death rates are plotted for the interpandemic years 1911-1917 (orange line) and for the pandemic year 1918 (green line).