Unfortunately, with Delta variant transmission rate and vaccine breakthrough probability, and the fact that no vaccine yet has a sterilization effect, we will not reach herd immunity. This is a done deal. Let's work on alternative strategy.
The existing mRNA vaccines were pretty close to having a sterilizing effect (unexpected and very good surprise) on the previous variants.
There is still hope that the Delta-specific updates (Moderna is already testing theirs) will restore that level of efficacy, and there's also ongoing research on intranasal vaccines which should work even better for that.