mRNA's mechanism of action is trivially simple. There's a known gene that codes for a known protein, and they create a snippet of mRNA to codify it. It doesn't change your DNA, it's not a virus, it's not able to replicate in any way. There aren't any unknowns waiting to be discovered. The mechanism is fully-understood and easy and safe.

The complications with mRNA vaccines like this have to do with keeping the mRNA intact during delivery and getting it into the cell so the protein gets built. That's the hard part, and the focus of all the patented engineering that differentiates BioNTech and Moderna vaccines. And the delivery mechanism, while complicated, doesn't involve anything genetic; it's a mechanical problem.