the reason they don't do trials every year for the flu vaccine is because it is a variation of the same thing every year. they spend 3 months discussing what are the most likely 3 strains to enter the population, then form the vaccine with dead forms of those 3 strains. they use the same method every year, only the strains are different (so it is not a new vaccine every year, in effect). the h1n1 vaccine is the same thing as the regular flu vaccine except that it will contain h1n1 as the dead virus. i am not sure why they are running trials- maybe to allay some public fears.