1510

First well-documented influenza epidemic in history—although descriptions of outbreaks that sound like this disease go back to ancient times.

1557–1891

At least 20 more major influenza epidemics.

Aug. 1914

World War I breaks out in Europe. U.S. proclaims its neutrality.

Apr. 6, 1917

United States enters World War I on the side of the Allies. Over the next 18 months, 4 million American men will be called up for military duty.

First Wave of the 1918 Influenza Epidemic

Jan.–Feb. 1918

Serious flu outbreak in Haskell County, Kans.

Mar.–May 1918

Soldiers from Haskell County bring the flu to Camp Funston, Kans. From there the flu spreads nationwide, infecting both soldiers and civilians. It is very contagious, but cases are generally mild.

Apr.–June 1918

Flu travels to Europe with U.S. troops. By June, it has spread across Europe and around the globe.

June–July 1918

The first wave of the epidemic gradually dies down.

Second Wave of the Epidemic

Aug. 4, 1918

Military physicians in France report the rise of a new, more virulent strain of influenza, which soon attacks soldiers and civilians throughout Europe.

Aug. 30, 1918

First major outbreak in the U.S. of the epidemic’s second wave—at Commonwealth Pier, a naval base in Boston. The disease quickly spreads to surrounding communities. Meanwhile, the second wave is also moving from Europe into Africa and Asia.

Sept. 11, 1918

Sailors transfer from Commonwealth Pier to training stations near Chicago, Philadelphia, and Seattle. Each of these facilities is soon facing its own epidemic, and within days the disease spreads to civilians in the cities nearby.

mid-Sept. 1918 on

As flu sweeps across the country, American communities—assisted by the U.S. Public Health Service and the American Red Cross—mobilize whatever resources they can to combat the epidemic.

Sept. 26, 1918

Recognizing that flu is paralyzing America’s military training camps, the Army Provost-Marshal cancels the next draft call, which had been scheduled for early October.

Oct. 7–Nov. 2, 1918

Flu mortality peaks in the United States and around the globe, after which the second wave of the epidemic starts to decline.

Nov. 11, 1918

Armistice Day. Large crowds congregate in the streets to celebrate the end of the war.

Third Wave of the Epidemic

Nov. 1918–Jan. 1919

In many communities around the world, the number of new flu cases starts to climb again, heralding the arrival of the third wave of the epidemic.

Apr. 1919

Third wave abates.

Afterward

1930s

Scientists identify a direct descendant of the virus that caused the 1918 influenza epidemic.

1941

U.S. Army develops the first effective flu vaccine.

1946, 1957, 1968

A series of global flu epidemics.

1997

Major outbreak of avian flu (H5N1) in southeast Asia. Few human cases but a high mortality rate among those affected. Repeated avian flu outbreaks in the years that follow.

2005

Team led by virologist Jeffrey Taubenberger works out the entire genetic sequence of the 1918 flu virus.

2009

Flu breaks out in Mexico and the southwestern United States. Although the symptoms are mild, the epidemic spreads around the world, ultimately reaching more than 200 countries.

2013

New strain of avian flu (H7N9) emerges in China. Like H5N1, it is deadly for humans, but does not seem to pass easily from person to person.