The Spanish Influenza Epidemic of 1918 was a pandemic of the lethal Spanish influenza between 1918 and 1919. It was the most severe outbreak of the 20th century.
After some time, the virus mutated into a more lethal strain and a second, more severe form emerged in August 1918. In India, at least twelve and a half million deaths occurred. The United States of America suffered approximately five hundred fifty thousand deaths, and a total estimated thirty million people died throughout the world. (PROSE: Casualties of War) Colonel Hugh Curbishley claimed to have been crippled due to the outbreak. (TV: The Unicorn and the Wasp) Speaking in 1965, Venessa recalled that the outbreak killed "something like" 5% of the human race; this was corroborated by Jack Harkness, who acknowledged that he was there. (TV: Children of Earth: Day Four)