'Spanish' Flu pandemic.

The first case of 'Spanish' Influenza was recorded and thus began the two waves of the 'forgotten' pandemic that possibly infected 500 million humans, killing between 50 and 100 million. The global mass movement of armies during the latter years of the First World War are believed to have contributed to the spread, mutation and lethality of the virus. It was speculated that the weakening of the soldiers' immune systems through poor nourishment, the stresses of combat and the unknown effects of chemical attacks all created a susceptibility to the contagion.

The wartime censors on both sides deliberately supressed any reporting of outbreaks and it was only because its lethality was freely reported in Spain that it became known as the 'Spanish' Flu.