I don't know about the quickness of the infection.
I do know that we don't know how many have had it, because a large % have no symptoms or mild enough to not even realize they have it. So that
throws off any calculations, since we're comparing fatalities, or bad non-fatal illnesses to only confirmed cases. And given how little testing has occurred the confirmed cases isn't = to the total.
I do know that in Italy, 99% of the deaths are of folks with one or more underlying medical issues (diabetes, heart stuff, etc.) That from the Italian Health org. The CDC has said that 90% of the fatalities in the US is the same.
It's an unhappy situation for me. I'm US born, but with dual US and Italian citizenship. And, though I don't live in NYC, I was born there and have family there including a son and grandkids. So, my heart gets tugged. But, it also gets tugged by our economy getting crushed because we've way over-reacted.