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.
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.
What are the assessments of the HN crowd?