Actually, most of those flu's will probably never be able to attain the ability to pass to humans.
As for this swine flu, while I do think its a medical emergency that needs to be carefully monitored, I don't think its going to start a full fledged pandemic. For one thing, several flu medications have been found to be effective in treating it. That's very important. Second, all of the swine flu cases seen outside of Mexico originated there, in most cases the poeple who became ill traveled there at some point. It will be crucial to see if this flu can now be spread from these already ill people to others who are totally unconnected to the outbreak. Third, this flu has been extremely mild in every country except Mexico. That's the only place where there have been deaths, and where there has been the most illness.
Lastly, keep in mind that all of our past pandemics occurred when medical care was rather primitive. This is 2009. Medical care has come so far since the last pandemic in the 60's that its hard to imagine another pandemic occurring, except under the most severe of circumstances.
