You might find this article interesting: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5906799/ - especially under safety. I can see how some of those concerns might be present especially given that we didn't have large scale human mRNA tests.
Take it with grain of salt, since I have no knowledge about this, but I found this [0] channel on youtube very helpful on covid related info.
It's a new type of vaccine that's never been been approved for use in humans before, was rushed through development and testing, for preventing a disease with a fatality rate between .3% and 1%. I'm worried. I hope there's a successful adenovirus vaccine.