Not very. So, far cov-19 has mostly not infected a terribly high percentage of the population , with the exception of some places in Lombardy where it likely reached saturation( > 60%). NYC, about 20%.
Spain: 5%. Major League Baseball employees : 0.75%.
Percentage infected in the US has to be lower than in Spain: I’d guess something like 3%. So far, > 80,000 dead out of that 3%. What can we expect if A. we let it rip and B. herd immunity is at ~70% ?
The people arguing that it had already spread very far and had a very low mortality were wrong, like I said a while ago. Obviously wrong, to me, and to a few others that could actually do the required back-of-the-envelope calculations. This means, by the way, that the IFR was > 1% in Spain. Not obvious to the authors of that Stanford study, though: I thought that surely they had been paid off, but they were apparently just dense.
But old bullshit is being replaced by new bullshit, due to popular demand. The new notion is that a more detailed analysis of viral propagation ( roughly, considering networks of fast-spreaders) suggests that it is possible to achieve herd immunity at far lower percentages infected than simple SIR theory predicts – instead of something around 70%, more like 15 or 20%.
Sometimes people are saying something not altogether crazy: like saying that we could achieve herd immunity at fairly low % infected if we made significant social changes (masks , distancing, Scotchguard everybody) that interfere with viral transmission and stuck with those changes indefinitely. When repeated, people usually leave out those behavior-change details and suggest that, soon, we will all be dancing in the streets. Swinging, swaying, records playing. Or, they’re saying that a more complete analysis predicts 60%, instead of 70%: might be so. But we know that simple SIR models have worked decently in the past – they can’t be too far off.
But mostly they’re just saying that herd immunity has to be possible at low incidence because it’s GOTTA be, the same reason they knew that Cov-19 was ‘just another flu’. The Swedish government is saying that Stockholm is close to herd immunity: they’re lying.
The numbers in Lombardy falsify this. But, go ahead, explain that Italians are special, not subject to same principles as other human populations.
These low numbers show that we’ve controlled the spread to a very significant degree. But we surely seem to be getting ready to stop doing so:
Guess what happens then!