It's not the percentage of intact mRNA that's the problem, it's what the other bits of mRNA happen to do.
Otherwise, the mRNAs aren’t present in high enough quantities to do significant signaling or silencing things, and it’s going in the deltoid... not really a medically interesting place. You could inject 1mL of dilute HCl there and it wouldn’t be a big problem.
no cytoplasmic nucleotide transport signal and it gets degraded quickly.