Just for my own information

The 1918 Spanish Flu Pandemic lasted from March 1918 to June 1920, spreading even to the Arctic and remote Pacific islands. It is estimated that anywhere from 50 to 100 million people were killed worldwide, or the approximate equivalent of one third of the population of Europe. An estimated one third of the world (500 million people) became infected.- Wikipedia
The 1957 pandemic of Asian flu lasted from late February 1957 until February 1958. Estimates of worldwide death rate varies widely depending on source, ranging from 1 million to 4 million.
For reference, about 36,000 people die in a typical flu season.