The US and Europe haven't vaccinated for smallpox since the early '70s and routine vaccination wrapped up globally in the mid-'80s, so, for many... absolutely nothing.
I used to be amused when period pieces would show actresses (particularly European) in sleeveless attire with their smallpox vaccine scar, three feet tall in the closeup shots.
Turns out smallpox vaccines are a lot older than I thought. They might have not looked exactly like that in Victorian England, but an iteration of it did already exist. Guess that's why they cover up tattoos but not smallpox scars.
More generally, if you told the immune system to ignore a still existing disease, it would probably be defenseless if/when you actually got infected by it.
Or could the immune system maybe override this if you got really sick?
Add I understand it, it's not about actively ignoring something. Rather, the immune system somehow learned to react more strongly to specific antigens, and undoing that. The natural immune reaction should still happen when encountering diseases, and not when encountering normal body tissues.
It's possible to use such tricks to actively shut down the immune system, but you either have to incorporate it into the disease (which actually happens in nature) or take that medicine continuously.
Very cool, but what would happen if that molecule was small pox?