Everyone saw the study from yesterday, that 24 hours after infection Delta generates viral loads 1000x the original A/B strains out of Wuhan? This is what's driving breakthrough infections among vaccinated, including some on the more serious side of mild, like
@Disney Experience. And reports of clusters, like the one in Singapore, being started by vaccinated people. While vaccinated people have lower viral loads, even a 99% less viral load still means they could be carrying a load 10x the thing that started all of this. That's what happens when you go from garden hose to fire hose.
We should expect guidance to change because the virus changed, and I doubt LA will be the only mask mandate that gets reinstated (although most places will likely go with "recommended.") If your vaccinated, you're still more likely than not going to be fine. But the bits about vaccinated people playing no role in transmission? I expect that will be re-evaluated. Still much, much less of a role, especially in small groups of vaccinated people. But long exposures, in crowded areas.