Influenza Pandemic of 1918–19

The influenza that spread throughout the world from 1918 to 1919 was one of the deadliest pandemics in human history. It sickened at least one-quarter of the world's population, 2 to 4 percent of whom died, usually from complications of pneumonia. Influenza killed more people in one year than World War I had killed in four: the flu killed 40 to 50 million compared with 9 to 12 million war dead. The pandemic came in three deadly waves: the first in the spring of 1918, the second and most deadly wave in the late summer and fall of that year, and a third, weaker but still lethal, wave in early 1919. In the United States, an estimated 25 million people became ill and 675,000 died. The influenza pandemic followed wartime [Page 370]transportation routes across oceans and continents, heaping misery on a world already struggling with the mass death and destruction of modern industrial warfare.

This map shows the sequence and path the influenza pandemic of 1918–19 took across the country.

Like the common flu, the 1918 influenza had a short incubation period, a high sickness rate, and was highly contagious, spreading from person to person most often in airborne droplets. This virus, however, had unusually severe symptoms. A quick onset of illness, high fever, severe headaches, torpor, nosebleeds, a blood-producing cough, and cyanosis—a blue cast to the skin caused by lack of oxygen in the blood—often enabled public health officials to pinpoint to the day the flu's arrival in a community. The 1918 flu was also unusually lethal, especially for young adults. Whereas influenza usually kills only the very weak in a population—the youngest and very oldest—and creates a “U-shaped” mortality curve, the 1918 virus was also deadly to people ages 20 to 40. It killed both the weakest and the strongest in society, producing a “terrible W” curve of high mortality for the young and old at the extremes of the demographic spectrum, with an unusual peak at its center.

Medical professionals did their best to save flu patients, but in an era before virology and antibiotics, they lacked effective tools. Treatment included bed rest, a light diet, aspirin for fever and pain, and keeping the patient warm in hopes of preventing pneumonia. Recovery usually occurred after a few days unless pneumonia, which was often lethal, developed.

The origin of the influenza of 1918 has long been a mystery and the virus responsible was not identified until 1997. Influenza apparently first appeared in March 1918 in the American Midwest and from there spread to soldiers in several U.S. Army training camps. The virus then traveled to Europe, probably aboard troopships, to the Western Front where in May and June it sickened thousands of soldiers but killed few in this first wave. In the wretched conditions of trench warfare, however, the virus flourished, mutating into [Page 371]an especially virulent strain that exploded worldwide in August 1918. This deadly second wave of flu appeared simultaneously in the Atlantic ports of Boston, Brest (France), and Freetown (Sierra Leone), once again following troops and the increased trade generated by the war. From these points (and probably others), it spread throughout the globe within weeks.

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