If you take a pill and you react to it, the reaction doesn’t go much beyond a couple days.
It gets metabolized and excreted from the body in pretty short order.
You get an injection, and the stuff is in there to stay. There’s no way of sticking another needle in and sucking out the offending substance.
So you’re stuck reacting to whatever you were injected with as long as it remains in your body.
THAT is why I am NOT taking any vaccine I don’t need to for survival.
Good, rational thinking.