I think population density also plays an important role. There seem to be various mechanisms that undermine the immune system (broad tolerance, T-cell depletion due to specific tolerance and multiple infections and the likely existence of super shedders) and when many people are packed together it makes it easier for pathogens to spread.

Somehow the overview above between brackets makes sense to me. It is not just the vaxxed but also the unvaxxed that need to be careful athough the unvexxed are better of