The potential health problems are unknown. For example, we are assuming that Myocarditis/Pericarditis is extremely rare, or at least more rare than in a viral infection. Do we really know that, for all age groups and all vaccines? I have doubts, we are still in the discovery phase:

https://www.reuters.com/world/us/us-probing-moderna-vaccine-...

The spike protein is not necessarily a problem, but both NLP and viral vectors have never been rolled at the current scale. TTS seems to be particular to viral vectors, Myocarditis/Pericarditis more so to NLP.