mRNA vaccines are, of course, just the absolute tits - but they're a tiny proportion of modern vaccines and the very first ones are one a few years old, created to treat COVID. But yeah, 100%, we don't use the virus in the vaccine! Even the first ever vaccine was (as you will know) not created from the disease it was meant to treat, but from one similar enough that it gave protection to the other. And smallpox doesn't exist any more so, well, that worked out pretty well didn't it. You don't give someone the virus to stop them getting that virus, but you might well give them a virus, in an attenuated form of the target