Woah. My first instinct was honestly to say that sounds like bullshit but apparently it isn't and research into substance specific opioid vaccines has been happening for at least a couple of years.
It probably isn't permanent, most vaccines aren't completely, but it does sound like it would be effective for a long time, and maybe would even confer some lifelong protection even if immunity waned somewhat.
I don't know if you'd be setting up a reservation to use it again or not by not getting this but speaking as someone who has never used fentanyl (to my knowledge) and has no real interest in using it (highly doubt it's anything special, never heard anyone say that it's anything special, obviously also potent enough to be fairly dangerous) - if I lived somewhat where fentanyl cuts to my Drug Of Choice were a real risk, and I had the option to get this vaccine, I would 100% get it, it seems like a huge upside (protection against one of the most frequently lethal cuts in recent history) for almost no downside (it's highly selective to fentanyl, so other opioids would still work).
I'm not saying that if I had easy access to fentanyl of a known purity and ideally formulated into pharmaceutical grade pills or something rather than it's dangerously potent raw form, I wouldn't give it a try out of curiousity, I probably would, but if I never use fentanyl in my life I'm finding it hard to see that I'd care all that much. And I would kind of like the idea of being actually immune to a substance that otherwise could quite easily kill me.
Is fentanyl specifically really that unique and special, in your experience, that you'd find the idea of not doing it ever again concerning? Could you describe what it is about it that you couldn't get out of any other opiate/opioid? Am honestly curious, my general impression was that very few people would use fentanyl if given the choice of a better opiate, like heroin for example, I guess, to pick the most obvious one.