If it can't replicate as well in you, you significantly reduce the ability for it to spread via you typically. Herd immunity fro that perspective is about redu

If it can't replicate as well in you, you significantly reduce the ability for it to spread via you typically. Herd immunity fro that perspective is about reducing spread to the point that outbreaks don't spread from local groups because the R value is low enough, even taking into account the few people who can't be immunized.