[londons_explore]

Many vaccines become 'perfect' by causing the disease they treat to die out in the local community.

It doesn't need to be perfect at the individual level to cause that - and in fact many vaccines at the individual level actually have pretty bad metrics - like for example only preventing half of cases.

[TylerE]

You're seeing this in vivo with polio - POLIO!! - starting to make a reappearance in some of the more extremist Hassidic communes in NYC. Those groups do not get vaccines.

[bigbillheck]

Polio's complicated because of the differences between the vaccines meaning that external vigilance will be needed even with 100% coverage.

[LorenPechtel]

This is how vaccines are expected to operate. You don't need perfection, just enough to drive the reproduction rate below 1.

However, note that this is in a population where there will no doubt be leaks. Even if everyone in the area got the jab that doesn't mean they won't have sex with people who didn't. Thus an infection rate of zero is a good showing.