Spanish Flu

In 1918, a strain of influenza known as Spanish flu caused a global pandemic, spreading rapidly and killing indiscriminately. Young, old, sick and otherwise-healthy people all became infected, and at least 10% of patients died. Estimates vary on the exact number of deaths caused by the disease, but it is thought to have infected a third of the world's population and killed at least 50 million people, making this respiratory virus the deadliest pandemic in modern history. Although at the time it gained the nickname "Spanish flu," it's unlikely that the virus originated in Spain.