I firmly believe that to be part of the answer, our "CDC" also said as much in 2020. Lots of clusters of infection popping up in parts of the population that lives very tightly and in large family groups, and those are predominantly immigrants and their kids. Im not sure how it looks in the third wave though. That and the care homes for elders were a big problem early on, but lately it seems to be a more general spread which is probably even harder to stem.

I have not yet seen anyone try correlate socio-eoconomic status and/or overcrowding to infection in a nice way?