> but testing the thing for safety and efficacy took months
What kind of tweaks were made from "the version they threw together in a weekend" to "the version that is in production now"? What's a typical "mRNA" feedback iteration loop like?
I'm not sure if there were changes in the sequence at all necessary during testing, however if you align the sequences given in that link from Biontech and Moderna, you see they encode the exact same protein (which is of course necessary). However the RNA sequence contains quite a few differences between the companies, they often use a different codons. This could be to make the translation more efficient, and can be a thing to optimize.
