More information about the Spanish Flu, for those who somehow haven't heard of it, is available on Wikipedia: http://en.wikipedia.org/wiki/Spanish_flu

Extra nice quotes:

The global mortality rate from the 1918/1919 pandemic is not known, but is estimated at 2.5 to 5% of the human population, with 20% or more of the world population suffering from the disease to some extent.

This pandemic has been described as "the greatest medical holocaust in history" and may have killed more people than the Black Death.

Another unusual feature of this pandemic was that it mostly killed young adults, with 99% of pandemic influenza deaths occurring in people under 65, and more than half in young adults 20 to 40 years old.