Brian - it would be easy for me to get way over my head quickly, and I'd bet there are others here with much better science training and knowledge that me... but I'll take a high-level stab at it.
First, using mRNA (messenger RNA) isn't a totally new concept, but as it has been explained to me our ability to use the concept to design treatment/vaccine approaches is what is new and developing rapidly. I'm in the cancer field, for example, and some of the mRNA possibilities for targeting certain cancers are and have been being researched and tested that have some very exciting possibilities. So, timing was good for this virus in the sense that our knowledge and our capability to act on that knowledge had reached a point where some theoretical solution approaches had been conceived and could be tested reasonably quickly. Second, development of these approaches, once initial hypotheses proved out, could be scaled for broader lab testing more rapidly than traditional vaccine approaches. So, in car parlance, if 60mph is where human studies begin, the 0-60 speed was faster than ever thought possible. Then, as I understand it, the research took a more traditional path and timeline of testing for safety, then testing for efficacy (blinded, etc.), follow-up, and data analysis. At this point, the evidence was strong enough to convince independent and government authorities to issues emergency use authorizations for use - where in a less urgent situation those bodies might have preferred to do more testing and longer term follow-up over subsequent months. So we got a speed pick-up there, too. And, finally, at some point in the research portion and well before EUA, when early evidence was pointing to the positive, someone in authority had to agree to fund production so that the drug companies wouldn't wait for approval to start producing in mass.
