THE FLU VACCINE IS NOT AN EXACT SCIENCE. INFLUENZA HAS BEEN AROUND FOR CENTURIES AND EVERY YEAR, WE NEED TO GUESS WHAT FLU TO PROTECT AGAINST. NEW STRAINS COME ABOUT OFTEN, AND EACH ONE REQUIRES AN ALTERED VACCINE THAT WILL SURPRISINGLY OFTEN NOT WORK. SO TELL ME AGAIN THIS VACCINE IS SUPPOSED TO BE A ONE-SIZE-FITS-ALL FOR FOUR DIFFERENT STRAINS, AS LONG AS YOU GET A BOOSTER THAT IS SUPPOSED TO DO THE SAME THING AS THE ORIGINAL.