The Spanish Flu Pandemic (1918): In 1918, the garden-variety flu mutated into a deadly virus. This new, lethal virus, which became known as the Spanish flu, swept around the world in three waves, killing an estimated 50 million to 100 million people (the equivalent to 2.7 to 5.5 percent of the world's population).
See full article: The 1918 Spanish Flu Pandemic
