'Spanish flu' pandemic
The 1918 influenza pandemic was caused by direct transmission of avian influenza to humans and killed an estimated 50 million people worldwide in the aftermath of the First World War.
The first outbreaks were reported in American military bases in March 1918, moving to Europe in April / May and reaching Asia by June. The pandemic is estimated to have infected 50% of the world's population, with the mortality rates highest among young, healthy adults.
Approximately a quarter of the British population was affected. The health care system was overwhelmed but there was no treatment.
Public Health England.
Influenza Pandemics - history.
The National Archives; nd.
The Spanish Flu Pandemic of 1918.
Historic UK; nd.