From Wikipedia, the free encyclopedia Pandemics The 1918 flu pandemic (the "Spanish flu") was an influenza pandemic. It was an unusually deadly and severe pandemic that spread across the world. Historical and epidemiological data are inadequate to identify the geographic origin.[1] Most victims were healthy young adults, in contrast to most influenza outbreaks, which predominantly affect juvenile, elderly, or weakened patients. The flu pandemic was implicated in the outbreak of encephalitis lethargica in the 1920s The pandemic lasted from January 1918 to December 1920, spreading even to the Arctic and remote Pacific islands. Between 20 and 50 million died, making it one of the deadliest natural disasters in human history.[1][4][5][6][7] Using the higher estimate of 50 million people, 3% of the world's population (which was 1.86 billion at the time[8]) died of the disease. Some 500 million, or 27%, were infected.