In 1918, a new influenza virus appeared, right in the middle of World War I. People called it the Spanish flu. It was later known as the H1N1 virus, or swine flu.

At the time, that conflict was called the War to End All Wars, or the Great War. It was so terrible, people all over the globe thought the end of the world was coming – and then, the 1918 flu pandemic came along.