[loveistheanswer]

>mRNA technology has been in development for many years with much of the effort going into studies of human safety.

Have there been any long term human trials of mRNA vaccines?

[m0llusk]

Yes, though that might depend on your definitions of both long term and vaccine. There is actually a quite interesting body of literature surrounding these developments, so it might be worth doing some searches and some reading.

[loveistheanswer]

Do you have any sources for long term mRNA vaccine trials on humans?

My searches seem to indicate there are none, other than the preliminary, limited scope short term trials