In the worst-case scenario, bird flu, a.k.a. H5N1, will infect 2 billion humans, and kill 1 billion of them. (Yes, billions). I hope I don't have to remind you of the impact of that. It will make Katrina seem like nothing worth mentioning. If it happens, the world will basically be shut down. The economy would take at least a decade, if not more, to recover.
Hair on fire alert!!
Right, but it's not looking that way - people had the same concerns about SARS, which has basically died out. "Only" 93 people have died from the bird flu. It could become a pandemic, but I haven't seen any evidence of that yet.