1)I think a fair case can be made that certain US regions, especially NYC, have achieved herd immunity. I'll lay out the key elements of that case over the next few days, seeking support or refutation from others. Here I'll focus on one question: Can herd immunity be achieved...

2)...even though only a minority have been infected? Eminent epidemiologist Michael Osterholm @mtosterholm seems to think 60% must be infected & NYC is nowhere near that. But maverick epidemiologist Knut Wittkowski (who firmly believes there's herd immunity in NYC) tells me:...

3)..."There are 3 different mechanisms by which we can become immune. And they're mediated through antibodies against infection w/the particular disease, antibodies against infections with similar diseases--and then we can have T-cell immunity, where we harbor T-cells,...

4)...not antibodies, against that disease. And all 3 forms can contribute to immunity." So the first kind, direct immunity, might arise from a 20%-25% infection rate, while the other two kinds can do the rest to achieve herd immunity. Mayo Clinic Dr. V Rajkumar @VincentRK...

5)...& Stanford Biophysics Prof. Michael Levitt
@MLevitt_NP2013 seem to agree w/Dr. Wittkowski. Are there others? Contrast this with statement from the NYC Mayor's Sr Advisor @DrJayVarma: "The vast majority of New Yorkers weren't infected. So the most likely explanations for...

6)...our current situation are, as the mayor pointed out, physical distancing, wearing face covers, good hygiene — and the massive increase in testing that's tied to identifying contacts and safely separating cases with contacts." Having seen photos of grubby-looking people...

7)...w/no face coverings, who slept in tents in front of City Hall, I gotta wonder about the uniform practice of good hygiene! And this NY Times article questions the effectiveness of the contact tracing. Yet NYC's numbers remain quite low. Herd immunity? https://www.nytimes.com/2020/07/23/nyregion/coronavirus-testing-nyc.html