We have enough short-term data on the mRNA COVID vaccines and long-term data on other mRNA vaccines to make emergency use authorization a reasonable decision.
And that was written in December 2020, before the Pfizer and Moderna vaccines had been administered to millions of people.
If there are, they would be far less than the long term effects of actually catching the active virus.
When a virus invades your cells it unravels itself and it's mRNA goes to the host cell's nucleus where it destroys that cell's DNA and then assembles copies of itself out of the scattered nucleotides. The viral copies then invade adjacent cells repeating the process exponentially (hence the term "going viral"). If one's immune system needs time to "train" itself to recognize and fight the virus, the battle could be lost and vast numbers of those mRNA strands will be created.
The vaccine is an inert string of mRNA which is incapable of infecting a cell as it does not have the protein coat. It's purpose is to train one's immune system to later recognize and destroy the virus before it can replicate itself excessively.
This was the long way of saying you'll have a whole lot more of that mRNA in you if you get an active infection than you'll ever have from receiving an inoculation.