1. MRNA vaccines have not been approved for use before (outside of clinical trials) They have been srudied for over a decade, developed for things like flu, Zika, rabies. It's just that this is the first application they've worked through. It carries no live virus, irt doesn't enter a cells nucleus. They have worked on this, developing new technology, delivery systems for a decade. It is new, not unknown!
2. We don’t know if this vaccine stops you getting the virus, just that it lessens the symptoms in some cases (so I’ve decided at this stage the benefit is not worth the risk for me) It won't be offered to you. As has been discussed her, forever it seems, it has some issues that restrict access.
3. I understand why this vaccine has been developed in record time (unlimited funding, and the brainiest brains working collectively etc.) but none of that replaces time. At this stage we just don’t know what the long term side effects are. Hope there won’t be any serious ones, but the fact remains we don’t know. OK! That's the same with every vaccine, every medication ever. There have been some trials, as deemed essential by the MHRA, EMA etc etc etc and have, apparently, met all the USUAL standards. Time is maybe not as important as you think in understadning the potential issues
This trial isn’t even scheduled to end until 2023. Don't do that! The extended timeline is to do what you say is currently lackng... to collect longitudinal data to support further testing, improvements etc.
There are legitimate issues to consider. But they seem to be around efficacy and longevity of the vaccine itself. Which will be the same for every vaccine currently in development. But there is a vast swathe of epidemiological data out there... I am sure any scientist involved in that part of the assessment and testing will have a best guess that will be far more informed than anyone posting heer, writing doom and gloom pieces in the media and anyone unravelling across SM!