The 1918 flu pandemic (January 1918 – December 1920) was an unusually deadly influenza pandemic which infected 500 million people across the world, including remote Pacific islands and the Arctic, and killed 50 to 100 million of them—3 to 5 percent of the world’s population at the time—making it one of the deadliest natural disasters in human history. To maintain morale, wartime censors minimized early reports of illness and mortality in Germany, Britain, France, and the United States; but papers were free to report the epidemic’s effects in neutral Spain (such as the grave illness of King Alfonso XIII), creating a false impression of Spain as especially hard hit— thus the pandemic’s nickname Spanish flu.
Most influenza outbreaks disproportionately kill juvenile, elderly, or already weakened patients; in contrast the 1918 pandemic killed predominantly previously healthy young adults. Modern research, using virus taken from the bodies of frozen victims, has concluded that the virus kills through a cytokine storm (overreaction of the body’s immune system). The strong immune reactions of young adults ravaged the body, whereas the weaker immune systems of children and middle-aged adults resulted in fewer deaths among those groups.
The close quarters and massive troop movements of World War I hastened the pandemic and probably both increased transmission and augmented mutation; the war may also have increased the lethality of the virus. Some speculate the soldiers’ immune systems were weakened by malnourishment, as well as the stresses of combat and chemical attacks, increasing their susceptibility.
Academic Andrew Price-Smith has made the controversial argument that the virus helped tip the balance of power in the later days of the war towards the Allied cause. He provides data that the viral waves hit the Central Powers before they hit the Allied powers, and that both morbidity and mortality in Germany and Austria were considerably higher than in Britain and France.
A large factor in the worldwide occurrence of this flu was increased travel. Modern transportation systems made it easier for soldiers, sailors, and civilian travelers to spread the disease.
In the United States, the disease was first observed at Haskell County, Kansas, in January 1918, prompting local doctor Loring Miner to warn the U.S. Public Health Service’s academic journal. On 4 March 1918, company cook Albert Gitchell reported sick at Fort Riley, Kansas. By noon on 11 March 1918, over 100 soldiers were in the hospital. Within days, 522 men at the camp had reported sick. By 11 March 1918 the virus had reached Queens, New York.
In August 1918, a more virulent strain appeared simultaneously in Brest, Brittany-France, in Freetown, Sierra Leone, and in the U.S. in Boston, Massachusetts. The Allies of World War I came to call it the Spanish flu, primarily because the pandemic received greater press attention after it moved from France to Spain in November 1918. Spain was not involved in the war and had not imposed wartime censorship.