Irrelevant so long as vaccination levels are as low as they are: there's no population where infection starts in a vaccinated person and spreads amongst the vaccinated only that we can reasonably track.

What we do know is that vaccinated people seem to be getting COVID Delta and spreading it to close contacts: but that's a self-selecting the sample too - people who are getting vaccinated are also vastly more likely to take adequate precautions if they get infected.