Probably the best example of this is the live oral polio vaccine. It's a bit risky (it occasionally reverts to being infectious) but in a population where polio

Probably the best example of this is the live oral polio vaccine. It's a bit risky (it occasionally reverts to being infectious) but in a population where polio is endemic it's much safer than letting polio keep circulating. (In places where polio isn't endemic, you get administered a totally inactivated vaccine by injection instead. They don't give everyone that one because it's more complicated to distribute, the oral one needs much less infrastructure)