As far as the why, maybe it is one way for DHS to be able to control people via quarantines and forced vaccinations. Here's an article on executive order 13375 which punishes anyone violating a quarantine order with a $250,000 fine and a 1-year prison term.
http://www.cbsnews.com/blogs/2009/04...y4975598.shtml
Here's the link that modified the order to include influenza. Almost like they were planning to create the virus for the setup:
http://edocket.access.gpo.gov/2005/pdf/05-6907.pdf