Consider the realistic uncertainty and probability from previous study of antibody dependent enhancement. It’s not proven that the mRNA therapy won’t worsen covid reaction in the long run.
What are you defining by "long run"? We're quickly moving into a year with mRNA therapies. I'm not aware of any instance of this occurring with previous vaccines, and we can't just say "well mRNA could be different" because if we do that all the possible "what-ifs" we quickly swing into the absurd.