The 1918 Spanish flu pandemic was caused by a particularly virulent strain of influenza virus. It infected 500 million people, caused around 50 million deaths, and its impact was so severe that global life expectancy fell dramatically. It claimed more lives than the First World War.
In their efforts to develop a vaccine, researchers at the time worked under the mistaken assumption that influenza was caused by bacteria, based on Richard Pfeiffer’s 1892 discovery of the “bacillus influenzae”, which today is known as the bacterium Haemophilus influenzae.
