I am not going to say that's impossible. I am going to say that there would be Nobel prize in medicine waiting if 2-year effects are both observed and explained.
Also, my child participated in a "long term" study on a childhood vaccine reformulation, and long term just means one year. So, if there were side effects outside of that period, it wouldn't be found from long term studies, it would have to come from some other research. Of course, small effects that show up years later is going to take a long time to pin down, and would have required a very large study group to notice statistically.
Realistically, if there is some negative side effect that takes years to develop and only affects a very small fraction of people, we won't know that it's related to any particular vaccine for a long time. And we'll figure it out from epidemiology studies, not from safety studies.