Origins of the Spanish Influenza pandemic (1918–1920) and its relation to the First World War

The virus which was responsible for the first benign wave of the Spanish Influenza in the spring of 1918, and which was to become extremely virulent by the end of the summer of 1918, was inextricably associated with the soldiers who fought during the First World War. The millions of young men who occupied the military camps and trenches were the substrate on which the influenza virus developed and expanded. Many factors contributed to it, such as: the mixing on French soil of soldiers and workers from the five continents, the very poor quality of life of the soldiers, agglomeration, stress, fear, war gasses used for the first time in history in a massive and indiscriminate manner, life exposed to the elements, cold weather, humidity and contact with birds, pigs and other animals, both wild and domestic. Today, this combination of circumstances is not present and so it seems unlikely that new pandemics, such as those associated with the avian influenza or swine influenza, will emerge with the virulence which characterized the Spanish Influenza during the autumn of 1918.