The 1918 influenza pandemic (January 1918– December 1920; colloquially known as Spanish flu) was an unusually deadly influenza pandemic, the first of the two pandemics involving H1N1 influenza virus.[1] It infected 500million people around the world,[2] including people on remote Pacific islands and in the Arctic, and resulted in the deaths of 50 to 100million (three to five percent of the world's population),[3] making it one of the deadliest natural disasters in human history.[4][5][6]