1 of 10
Influenza Fears, 1918
Surgical masks provide a measure of protection against a killer flu for American baseball players in 1918. That year—the final year of World War I—the Spanish flu took 50 million lives worldwide, at least three times as many as during the war.
Photograph by Underwood and Underwood/Time & Life Pictures/Getty Images

Influenza

See flu virus photos, plus influenza pictures, swine flu photos, and more in this flu gallery from National Geographic.