[TexasCajun]

I did get vaccinated as a kid but I do not get flu shots each year?

..and why would you need one each year instead of just once?

[srmorton]

..and why would you need one each year instead of just once?

There are many different strains of the flu virus and it also mutates very readily so it would be nearly impossible to create one vaccine that would protect you from all strains. This year's version is a case in point. The manufacturers incorrectly predicted which strains would be the predominant ones this flu season so the vaccine has not been as effective this year as in the past. It may lessen the severity, however, if you do get the flu. The virus that causes the common cold is another one which has so many strains that there most likely will never be a vaccine to prevent it.

[5th MEB]

Because the Flu Virus mutates and changes just about every year, and the shot you got last year might not work on this years virus.
That's not to say the vaccine manufacturers always get it right, this year the vaccine did not work on this years flu type.