RNA is a messenger. Typically it carries instructions from DNA to cells telling them how to produce protiens etc. The RNA based vaccines are completely synthesized in the lab. They "program" the T cells to produce a response. Ok, sounds good - cut out the middle man, no risk from use of live virus, faster development, etc.
But we're literally programming an immune system response from a completely artificial stimulus. As I understand it, RNA vaccine technology has never before been put to widespread use. What if the RNA "program" misfires on some people, some combination of DNA? What if the RNA is damaged or degrades, can the program change? How good does quality control have to be in the manufacturing process? Can a rushed into production process meet that? Can the RNA program morph into a very different immune system response? How will it interact with people who have an auto-immune disease? As I understand it, we're still discovering variations of auto-immune diseases, so we don't even know comprehensively what's out there for the RNA to interact with.
The RNA based tech is probably, hopefully safe but... There will be side effects as we move into trials of this experimental (that's the FDA's classification) drug. But it is not really a drug, not really a traditional vaccine, it is literally gene therapy. Using genetics to invoke a response. Too many unknowns, yet we're performing widespread trials now - not on a few thousand volunteers spread over years as we study and look for side effects... Nope, tens of millions are now in the trial group. History and Murphy's law says we don't get that lucky as to be 100% successful on the first try. There will be side effects, there will be unintended consequences. Some of these may not, probably will not show up for years. By hanging the "experimental" moniker on the vaccines the FDA is protecting the pharmaceutical companies from any kind of liability. So if a large percentage of the people getting one of these RNA vaccines develop psoriasis or arthritis or some such in a few years, gosh, that's just too bad, suck it up, we'll fix that next time around...
So in this trial for the new technology I am going to self-select into the control group and not take the gene therapy. I may take the J&J vaccine in a few years (it is a traditional vaccine) if it does not show any significant side effects and if covid is still a thing.
“...The RNA based vaccines are completely synthesized in the lab. They “program” the T cells to produce a response....”
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Your post is on the money up until it gets to the 2nd sentence in the above extract. That sentence is incorrect and is where your post goes “off the rails” and into the woods with all kinds of scary “what ifs”. Actually the vaccines’ mRNA simply goes to the cells’ ribosomes (the cellular protein manufacturing “machines”) where it serves as the blueprint for manufacturing the necessary antigens. From that point on the immune systems react to the antigens (by developing the needed immunity) just as they do with more traditional vaccines. That’s all the mRNA vaccines do... just provide a different means to provide the needed antigens. It’s not really scary.