Quote Originally Posted by Asta Kask View Post
I think it's fairly well established* that one of the influenza vaccines caused sleeping sickness. Of course, actually getting influenza carried an even greater risk for sleeping sickness, but that's rarely brought up.
It depends on the type of vaccine. Some forms of live vaccines can lead to developing the very disease it's supposed to prevent in certain people.

Serum sickness is also a thing, not to mention allergic reactions, although typically this is to trace production impurities rather than the vaccine itself e.g.allergic reactions to antibiotics.