People you know, in others words 2
A friend of mine lives in a shared house with 5 other people. All 6 are under 30, healthy, and have all been double vaccinated. 1 of them experienced symptoms, got tested and came back positive. All 6 had to self isolate for 10 days according to the COVID track and trace message. And in that time, 4 of the remaining 5 developed symptoms and had to isolate for a further 10 days from point of developing symptoms.
This is just 1 example.
On the flip side to that, my girlfriends mum got COVID early on, last year in April, and was in a terrible way for well over 4 weeks. My girlfriend and her dad who were in the same house as her, did not show any symptoms at all. Whether they contracted it and remained asymptomatic or miraculously managed to avoid it given how infectious it is, we will never know, as none of the standard testing traces for antibodies, so there is no way of knowing if you have had it and avoided the serious side effects, seemingly unless you die from it.
But the idea that transmission amongst vaccinated is a thing of the past is a false and dangerous assumption to make.