I guess what is commonly called sterilizing immunity. Immunity which is so effective that the illness doesn't occur and which makes it impossible to infect others.
In this context I was recently pointed to the story of Marek's disease [0], which went from a "quite low death rate" to "100% lethal" in a few decades. I think it's worth to know about this and have a long, hard think about the potential consequences of universal, non-sterilising vaccination. We might be locking ourselves into a situation with no escape.
I guess what is commonly called sterilizing immunity. Immunity which is so effective that the illness doesn't occur and which makes it impossible to infect others.