I find these numbers stunning. They're from a paper by Elizabeth Brainerd of Williams College and Mark Singer of California State University.
The 1918-19 influenza epidemic killed at least 40 million people worldwide and 675,000 people in the United States, far exceeding the combat deaths experienced by the US in the two World Wars, Korea, and Vietnam combined. Besides its extraordinary virulence, the 1918-19 epidemic was also unique in that a disproportionate number of its victims were men and women aged 15 to 44, giving the age profile of mortality a distinct 'W' shape rather than the customary 'U' shape, and leading to extremely high death rates in the prime working ages.
This brief historic background puts the influenza epidemic in context.
Only three epidemics in world history resulted in mortality approaching or exceeding the mortality caused by the 1918 influenza epidemic: the Plague of Justinian in the sixth century (100 million lives lost over 50 years), the Black Death of 1348-1351 (62 million), and the current AIDS epidemic (25 million)
You can read the "The Economic Effects of the 1918 Influenza Epidemic" here .