Originally Posted by Grapesoda

http://en.wikipedia.org/wiki/1918_flu_pandemic

The 1918 flu pandemic (January 1918 ? December 1920) was an unusually deadly influenza pandemic, the first of the two pandemics involving H1N1 influenza virus.[1] It infected 500 million[2] people across the world, including remote Pacific islands and the Arctic, and killed 50 to 100 million of them?three to five percent of the world's population[3]?making it one of the deadliest natural disasters in human history.