I agree that 2 billion is a high estimate, but I don't think it's impossible. I'd like to find some research that indicates which direction lethality goes when viruses combine and/or mutate... the info I've seen sounds hopeful that the H5N1 would attenuate when it became human-to-human tranmissable, but I haven't seen anything concrete - I don't know of any specific reason why it couldn't just as easily retain the same lethality or even increase.

You are correct in pointing out that most 'flu hits elderly and frail people the hardest, but this family of viruses (avian influenzas, of which the "Spanish Flu" was a member - H1N1) seems to target young, healthy people. The Indian Army experienced a 22% mortality rate among those soldiers who caught the 'flu., and over 20% of the entire population of Western Samoa died in the outbreak.

I don't agree with your idea about increased mobility conferring increased resistance, at least not to new strains - the whole reason a new virus is so dangerous it that it is new and populations haven't been exposed to it before.

In any case, yes, "we" - the world population - must be proactive. I guess the big question is the degree of proactivity. When the potential threat is so enormous, the preparations must be fast and extensive, but I'm not seeing anything like that.

The large number of deaths is a huge factor itself, but imagine the side effects: if, say, 10% of the workforce was seriously ill or even dead, how would that affect productivity?

How could the medical system even hope to cope with that many sick people, especially since a large number of health care workers will be sick as well.

Transportation systems would shut down, but probably too late to stop the spread.

It would change the world in a drastic way, and almost overnight.

Personally, I'm making plans to isolate my family if possible. If the weather is half decent, we will be as far from civilization as we can get if - when - things go bad.

Wikipedia has some excellent info on the subject.

(I'm starting to love Wikipedia - what other encyclopedia could have info in it that just hit the news that week?)