In 1918, many health professionals served in the U. S. military during WWI, resulting in shortages of medical personnel around the U.S. The economy suffered as businesses and factories were forced to close due to sickness amongst workers.

There were 3 different waves of illness during the pandemic, starting in March 1918 and subsiding by summer of 1919. The pandemic peaked in the U.S. during the second wave, in the fall of 1918. This highly fatal second wave was responsible for most of the U.S. deaths attributed to the pandemic.