in 1918, the Spanish flu pandemic started out exactly in this way: a few mild cases in the spring...then fizzling out...then reemerging much stronger and deadlier the following fall.
Yes, and nowadays we have much more knowledge on the spread of viruses and the evolving they do and the speed that they do it at. I did read an article on that scenario you describe above and if I can find it on line I'll post it. Nowadays we
expect viruses to evolve, it's no longer a surprise.
No vaccine is 100% effective,
Correct. Not always to do with the virus though. It can depend on the individual person. If they take a drug for something else it can interact with the vaccine and render it weaker.
H1N1 is spreading fast enough, almost 1000 cases world-wide and that will increase but the good news is the death rate is low with still only 26 people have died of it, all in Mexico apart from 1.