The question is, how to deal with it. Quarantine won't be of any use, by the time it's known, it will be too late. It's viral, which means there isn't really a treatment. If a vaccine can be developed, that would make an enormous difference, but that's not a sure thing, and the numbers required would be astronomical.
Best case scenario? The version that makes the leap isn't especially virulent and it's like an average flu. 35-50,000 dead. A more realistic answer? 350,000-5,000,000 (one to two odrers of magnitude worse). Worst case? Decimation. We'll see what happens.
But actually, wouldn't stockpiling the few anti-influenza drugs that are available reduce the death rate tremendously, at least in developed nations where people have access to them?
