Kluger, there are 2 parts here
1) vaccinated people are less likely to get infected and sick. It was 15x less likely for the original virus and right after vaccination (Phase 3 trials Nov 2020). It is less for Delta and 6 months out, probably 5x less likely.
2) even at this less likely rate, those who are infected are shedding less virus (this is what a just published paper above says) and thus are less likely to transmit.
High cases among vaccinated is due to people “rewarding” themselves – I am vaccinated, reducing my risk by 5x, now I can go to Turkey, increasing my risk by 10x.