Afaik, it was backed up behind a lack of safety trials.

Given how expensive those are to run, and how mRNA's primary benefit (speed of development) wasn't a competitive advantage in "normal" times, we had something that we thought was better, but no financial case to toss the gobs of money at it to get it certified.

If SARS-CoV-2 is remembered for one thing, it should be for finally breaking the logjam and "giving" us approved mRNA platforms.