If exposed to the virus when you have active memory cells for the spike protein. Your body has to remember it. So theoretically you get the vaccine, within the year you get exposed to covid and may end up with a stroke, a fall, or a lung reaction. If you got vaccinated and didn’t ever come across covid, or you were exposed to only small amounts of the virus you may have a mild inflammatory reaction. In the study they vaccinated and the next day put covid virus in their lungs directly.

I can imagine people who eat a diet high in plants and fish may not have any reaction at all.