Spanish Flu

Definition

The Spanish flu, also known as the 1918 influenza pandemic, was an unusually deadly influenza pandemic caused by the H1N1 influenza A virus. Lasting from February 1918 to April 1920, it infected 500 million people – about a third of the world's population at the time.

Related terms

Pandemic: An outbreak of a disease that occurs over a wide geographic area and affects an exceptionally high proportion of the population.

Influenza: A viral infection that attacks your respiratory system — your nose, throat and lungs. Influenza is commonly called the flu.

Herd Immunity: A form of indirect protection from infectious disease that can occur with some diseases when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby reducing the likelihood of infection for individuals who lack immunity.