I'm not sure if your sources really say what you imply that they do. Bergamo had a 58% COVID exposure rate as of last month, as determined by serology studies.
How many of those had a full blown infection? I suppose detectable antibodies suggests there was at least some level of infection, but a very mild infection plus rapid clearance in a plurality of the population fits with the sentence you quote. The other cites you provide basically show the same thing. Of course social distancing/lockdowns also help. Why not both? The reality is that there are two mysteries here:
i) a lot of people are relatively unaffected by the virus and serology shows they were exposed;
ii) a lot of people, even under very crowded conditions (USS Teddy R; prisons) just don't get COVID at all. 40% of those on the carrier simply never got it. How is that possible? The prison data is high if we take your the 80% upper level of your range, but you will expect to see those sorts of outliers in small datasets. This is particularly true where the early antibody tests were not very specific (i.e., relatively high false positive rate).
It was not my intent to imply anything about the severity of COVID infections, only that a 10-20% infection threshold is contradicted by several real world examples. While it is still possible that T-cells may have some immunological benefit against COVID, I don't think the 10-20% number qualifies as evidence of that.
How many of those had a full blown infection? I suppose detectable antibodies suggests there was at least some level of infection, but a very mild infection plus rapid clearance in a plurality of the population fits with the sentence you quote. The other cites you provide basically show the same thing. Of course social distancing/lockdowns also help. Why not both? The reality is that there are two mysteries here: i) a lot of people are relatively unaffected by the virus and serology shows they were exposed; ii) a lot of people, even under very crowded conditions (USS Teddy R; prisons) just don't get COVID at all. 40% of those on the carrier simply never got it. How is that possible? The prison data is high if we take your the 80% upper level of your range, but you will expect to see those sorts of outliers in small datasets. This is particularly true where the early antibody tests were not very specific (i.e., relatively high false positive rate).