Spanish flu research concerns scientific research regarding the causes and characteristics of the "Spanish flu," a variety of influenza that in 1918 was responsible for the worst influenza pandemic in modern history. Many theories about the origins and progress of the Spanish flu persisted in the literature, but it was not until 2005, when various samples were recovered from American World War I soldiers and an Inuit woman buried in the Alaskan tundra, that significant research was made possible.