I know there is a lot of controversy and fears over the mRNA vaccines. I felt this was a helpful page for understanding more about how the Pfizer and Moderna vaccines work.
University of Maryland Medical System
I can share that my own experience of the Moderna vaccine did cause a flu like reaction for about two days, but that seems to be the exception amongst the many people I have spoken to who have received it, and I work with seniors on an almost daily basis.