Is there data for that?
It can be inferred from the strong drop in cases of earlier strains through winter and early spring after vaccination efforts started. One might expect that to be true for delta (unvaccinated transmit more than vaccinated). If a vaccine provides protection it is reducing transmission.
https://www.healthline.com/health-n...ted-people#The-vaccines-and-the-Delta-variant
Delta is a very different critter than the strains for which we've been vaccinated. It's roughly twice as contagious and there's good evidence that it may produce more serious infections in terms of hospitalization rates. See new Lancet study of the outcome of 40K-50K cases where the strain was determined.