Check out "28 Days" and "28 Weeks Later". I think they were both superior movies to Will's Smith's work.
The U.S. is not prepared for a pandemic. It isn't that we don't have the capability. It is because we are not organized nor have the mindset to deal with it.
This is why health officials are so concerned about an influenza pandemic. The Avian Flu strain, H5N1, is nasty. If it crosses over to become a human virus the world in will be behind the power curve trying to deal with it. That is, unless we prepare to deal with pandemics as well as other disasters.
This type of preparation wouldn't necessarily stop a pandemic's spread so much as slow it and lessen its impact. Then the better technology comes into play to break the pandemic.
The point to remember is preparation. If prepared for disasters, the better technology of our civilization will not be overwhelmed. It will then enable us to make it through the hard times.