It created a overreaction of the immune system. Basically the victim's lungs would hemorrage and fill up with their own bodily fluids causing them to literally drown to death . It was a horrible death. People would be literally turning blue gasping for air as froth would spill out of their lungs and nose..... Multiply that scene by atleast 50 million and you have the Spanish flu. My grandfather had an indention on his rib cage because when he was 6 years old, he got the Spanish flu. His lungs started filling up with liquid, so a doctor took a scalpal and made an incision between his ribs into his lungs and then stuck a hose to drain the fluid. Gross, but true. His toddler brother died. Because young people have strong immune systems, the overreaction of the immune system was more acute and claimed more lives in the age range of 20 - 40. Having a healthy immune system worked against you with the 1918 virus. This Swine flu is cause for concern, because the majority of the people are young adults, whereas normal seasonal flu claims the young and old.....ones with weak immune systems. See the link?