Imagine that you had a Level 1 allergic reaction to peanuts all along, too low to ever actually notice the effect.
However, the spike proteins generated by the injection had the result of amplifying that allergic reaction, making it a Level 100 allergic reaction, very noticeable and very problematic.
I never had a milk allergy and one week after my J&J vaccine I had a severe milk allergy.
Red blotches all over my body and itched like a 2 day old sunburn.