“A lot of people are speculating that CV has been in the US for about the same amount of time as China. That would mean that herd immunity is already widespread, and help explain why fatalities are (currently) below projections.”
That theory has been pretty well dismissed as illogical and since we know the distribution of case severities we’re missing a few million corpses that would be required to support it.
Once again, from a doctor I’ve known basically my entire life, who has been a doctor for 45+ years, who would tell me if this was the end of the world or if it was a nothing-burger: Testing is going on in hotspots, predominantly, and returning about 10% positives in those places. The distribution of case severities is known from complete contact tracing and the data from South Korea and the Diamond Princess. 80% of cases are mild or asymptomatic and those are already in the stats (were, prior to NYC exodus). Asymptomatic cases can transmit the disease, so if there were some huge pool of asymptomatics out there, hotspots would be flaring up everywhere, rather than the cases being concentrated in a relatively small number of metro areas.
I, and I’m sure, my doctor friend, would be happy to be wrong.
We also talked about China and Iran’s numbers and concluded that if we were all good Muslim Communists we would be immune to the virus.
“...since we know the distribution of case severities...”
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You are right about that, though it will do little good that I tell you. Epidemiology is not a new science. Case distribution is governed by Farr’s Law and once again as it has for 180 years it is holding with the data. The current version is the IDEA equation, Infection Distribution with Exponential Adjustment. Let me know if you are interested but it is enough that you know there is science backing you up.
Now if there are two different germs out there both causing COVID-19...
Here’s from science direct:
https://www.sciencedirect.com/science/article/pii/S2468042718300101