10,000,000 is an economic formula. See the NPR link and discussion. I work in insurance and deal with mortality and risk all the time. Behind each death reported as a loss, there are people.
The big question:
we have 300,000 spare hospital beds in teh US for 330,000,000 people.
That means if more than 0.09% of the population suddenly requires hospitalization... they are not getting it. That doesn't even account for ICU/ventilators.
If you need medical attention and you don't get it, for the flu or COVID, your mortality rate skyrockets.
COVID has greater rates of hospitalization than the flu by about a factor of five to what I have seen. (CDC website data on flu for past few years, versus what I culled from a couple of studies posted here)
I think it was about 5% hospitalization rate.
300,000/.05 = 6,000,000
6,000,000 people get sick simultaneously at that hospitalization rate, and you have filled every single open hospital bed in the country.
We are at 1.4M confirmed cases now. with an r0 hovering a bit under 1, with lockdowns and stay at home orders. (based on website CC posted the other day)
Doesn't take much to tick that up.
that is the risk. Overwhelm the health care system, and you have a LOT of excess deaths.