Agreed, the flu vaccines every year are modified and changed, they have never been clinically trialled before they're issued to the general public. The flu changes every year. The main seasonal flu strains are H3N2 and H1N1, a 'swine flu' actually hits us every single year.

The thing that's novel about the new H1N1, I believe it's 'A/Mexico/2009', is the mixture of strains it comes from. However with a basic reproduction rate (in a non-immune population, this is the secondary infection rate for every 1 infected person) of ~1.7 it is likely that just basic hygiene countermeasures could defeat it. Even marginal immunisation of the population could do enough to bring the infection rate below 1.0 and cause the virus to die out.

For comparison the Spanish Flu had basic infection rates between 2-3. HIV/AIDS has 2-5 and measles, for example, is between 12-18. Smallpox had an infection rate of 5-7 and was wiped from the face of the earth.

Simply put immunization and hygiene programs are only intended to decrease the reproduction rate to near-1. When summer hits, the reproduction rate of influenza decreases dramatically.