That's not strictly settled science. The truth is herd immunity / lack thereof is well within the error bars of the vaccine efficacy / R0 estimates. We don't actually know, but it looks like the delta curve is peaking in some areas so my bet is in favor of herd immunity.
https://www.theguardian.com/world/2021/aug/10/delta-variant-...
https://www.theatlantic.com/health/archive/2021/02/herd-immu...