One other thing that may be having an impact is the increased public level of mask wearing. I know this is a sore subject with a lot of people on this board who claim they are medically unable to wear masks.
Data is piling up that while wearing most masks you aren’t protected from getting exposed to SARS CoV - 2, but you are far more likely to develop an asymptomatic or minimally symptomatic infection. Why is this ? It has everything to do with the viral dose to which you are exposed. If you get a big slug of this virus, you are starting off from a bad disadvantage with your immune system trying to play catch up from the beginning. This makes you more likely to develop the immune over compensation that results in the inflammation cascade that precedes severe COVID.
So if more people are exposed and develop immunity without even knowing it, population level resistance to this virus is steadily building without being realized. This is why we need a widely available, rapid and accurate test to quantify what is actually going on with herd immunity.