I don't think that's ever the case actually. It's just that the immunity conveyed by an active infection often is as good or better than what a vaccine would produce so there's no reason to apply the vaccine after an initial immune response. But just like some vaccines, after an infection you may need a booster later to maintain immunity.

Though for this specific vaccine the question is somewhat irrelevant. In this case, they are introducing an antigen that the underlying condition, MS would never cause to occur. This antigen activates regulatory cells which then supress the immune systems production of myelin targeting antibodies.

So in the case eof a normal vaccine, regardless of whether it is mRNA or not, the vaccine is conveying information to the immune system that you might also acquire through an active infection.

This vaccine however is conveying information to your immune system that no active infection would convey.

This all kind of answers my own question which would seem to be yes. As long as they can find an autoantigen that will stimulate regulatory cells which supress the problematic autoantibody producing immune cells. At least that is my read after mucking through the medical jargon.

Vaccine implies acquired immunity. Exactly same mRNA tech can potentially be used to treat cancer, cardiovascular or metabolic diseases, only the messenger RNA changes. It's probably called mRNA drug instead of mRNA vaccine even if the process is the same.

mRNA is tech that BioNTech is developing is completely digital. Once you have the RNA structure in the computer, you can just "print out" drug/vaccine using the same process without changing anything else.

Some vaccines are effective after exposure. The rabies vaccine for example is commonly given to people after exposure. As long as it is given soon, it can save your life.

If an auto immune disease damages your body but then it stops manifesting, your body will remain damaged. A medical treatment for the caused damage would be called a cure in this case. Vaccines that stop the auto immune response are not cures. A somewhat helpful example is pancreas transplant for type 1 diabetics: the person with the transplant would be "cured" (ie they'd have their own insulin production) but the auto immune disease will destroy the donor pancreas eventually. Hopefully in the future we will have complete, synergistic treatments that take care of both.

I think that this could be thought as part of a more general revolution: the know-how to program the immune system. This would include things like T-Cells therapy for cancer (1)

(1) - https://science.sciencemag.org/content/371/6525/145

I don't know why you're being down voted. mRNA and tcell programming is the future of medicine. We may literally not have to worry about pathogen borne, auto immune, or cancer ever again...