Question: Why didn't this flu "run its course" and die out during the summer?
Answer: Influenza in temperate regions of the world like the US normally does go extinct during the summer season and that's because the virus particles themselves survive very poorly in hot and humid conditions in particular. This year we have seen this swine flu not just persist over the summer but persist in fairly high numbers of people and probably what's going on is you've got a new strain of the virus that there's very little immunity to in the population as a whole. And that's probably allowing it to move from person to person a little bit easier than a normal seasonal flu strain would and persist.
And that means that we already have a fairly large number of people with the virus as we move into flu season which might mean that flu season comes on a little earlier this year than a normal seasonal year.