Is There a Smoking Gun in Vaccines?

At the beginning of the pandemic, experts who worked in this field said we don't know how to make a vaccine and we're not even close. Did they know that if you tried the effectiveness would wear off? Or did they not even know how to made the vaccines that we ended up making in less than a year? Were those experts aware of the less m r and a technique and whatever j j used? And did they know from their own experiences that if somebody made accene, its efficacy would trail off too quickly? Show me that document, or show me any investigative journalist who's looking for it. Here's where i'd start find the people who said in the beginning.