I stopped getting flu shots in the 1990s when I worked at a hospital. At the time it was no big deal to decide you didn’t want a flu shot; they don’t agree with some people. A nurse to whom I mentioned that I always got sick after a flu shot said (sanely): “Better just avoid getting a flu shot, then!”
The type of flue they vaccinate for each year is an educated guess based of what is emerging, often in China. So if a different flu becomes dominant the vaccine doesn’t work.