Earlier quoted context omitted.
There have been hundreds of millions of vaccinations. What unforseen danger is there at this point? Be precise.
What if there's unpredictable long term consequences? Like, turns out XYZ compounds gives cancer but that only become detectable after 18+ months. Although I admit I don't know if regular trials would uncover these either. I have no dog in this fight, I'm just providing a possible answer.
Off the top of my uneducated head, the one theoretical concern would be giving yourself an autoimmune disease, where your immune system attacks something it shouldnt. Like mistraining a model. Barring that, it seems general consensus is that long term consequences are infinitely unlikely.