Why do i need a flu shot every year, while many other vaccinations last years or even a lifetime?

You need a flu shot every once and awhile because not only could the medicine wear off but also because you need to be as safe as possible.
You need to always make sure your up to date on flu shots.
Source: My mom who gives flu shots :P

Well, I don't get flu shots and I'm fine. I've never had the flu my immune system hasn't been messed with by flu shots. I got sick after I got my T-Dap shot for 7th grade. So if i were asked to get a flu shot i would deny it.

Giga is the second highest prefix on the normal scale, the first is terra.