Spanish FluThe Spanish Flu Pandemic (less misleadingly called the 1918 flu pandemic) was a pandemic in 1918 and 1919 caused by an unusually severe and deadly strain of the subtype H1N1 of the species Influenza A virus (which apparently killed via cytokine storm, explaining the severe nature and unusual age distribution). In the 12 months of the pandemic, 50 million to 100 million people worldwide were killed.
Despite not having originated in Spain, the Allies of World War I came to call it the "Spanish Flu". This was mainly because the pandemic received greater press attention in Spain than in the rest of the world, as Spain was not involved in the war and there was no wartime censorship in Spain.
The global mortality rate from the 1918/1919 pandemic is not known, but is estimated at 2.5 – 5% of the human population, with 20% of the world population suffering from the disease to some extent. Influenza may have killed as many as 25 million in its first 25 weeks; in contrast, AIDS killed 25 million in its first 25 years. Influenza spread across the world, killing more than 25 million in six months; some estimates put the total killed at over twice that number, possibly even 100 million.
In the U.S., about 28% of the population suffered, and 500,000 to 675,000 died. In Britain 200,000 died; in France more than 400,000. Entire villages perished in Alaska and southern Africa. In Australia an estimated 10,000 people died and in the Fiji Islands, 14% of the population died during only two weeks, and in Western Samoa 22%. An estimated 17 million died in India, about 5% of India's population at the time. In the Indian Army, almost 22% of troops who caught the disease died of it.
While World War I did not cause the flu, the close quarters and mass movement of troops quickened its spread. It has been speculated that the soldiers' immune systems were weakened by the stresses of combat and chemical attacks, increasing their susceptibility to the disease