Not sure if the full information has been given so I'll just say this for you if you need it and for those who don't know it.

There are many strains of influenza, which appear to have a cyclical occurrence rate globally. The yearly flu vaccine is different from the one before and the one to come after because it contains vaccines for only those strains which are predicted to occur for that year.

It is not a live or dead virus on the vaccine. It does not shed. You cannot get flu symptoms from getting the vaccine, you were just already infected, or were exposed to an unvaccinated strain.

With any educated guess, they're wrong, pretty often. This leads to as belief that they don't really help protect you. They do, they're just not perfect. I'd rather wear a bullet proof vest which stops 80% of the types of bird than refuse it because it doesn't stop the other 20% of high power ammunitions.