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Comment by dannyw | Hacker News Reader

Perhaps the "something" is simply antibodies and herd immunity?

1. In April (!!), 1 in 5 NYCers tested positive for antibodies: https://www.nytimes.com/2020/04/23/nyregion/coronavirus-anti...

2. Given asymmetric social contact patterns, experts estimate that ~20% may be the threshold for herd immunity of COVID: https://theconversation.com/coronavirus-could-it-be-burning-...

I support looking at the science, and this means looking at it both ways; not just cherry-picking doom and worst case scenarios while ignoring best case scenarios.

We can't afford to let an "overabundance of caution" kill businesses and our economy, for good.

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It's not antibody immunity. That's why I said we don't understand. 20% is nowhere near enough to explain the patterns we're seeing.

The good news is that even though we don't understand it, the NY experience does point towards a potentially more muted second wave in areas which were hit hard the first time round (as long as they take precautions at least), but we just don't know enough to be sure - anyone who is sure about the outcome at this point is probably overconfident and wrong.

20% of the total population is probably 60% of choiceless and careless. Percentage of the population that are exposed to a potential Covid infection, either due necessity (essential workers and so on) or stupidity is much less than 100%.

Someone who has been barricaded inside of their home since February most likely doesn't have antibodies, but at the same time is not a potential Covid spreader.

20% is nowhere near enough to explain the patterns we're seeing.

... according to epidemiologists who have been utterly discredited, no. According to other epidemiologists (and just lay amateurs) who have built better models, 20% appears to be about the right threshold when taking into account non-homogenous social mixing and t-cell immunity.

But you don't really need anything fancy to figure this out. Just look at the observed data, messy and contradictory though it is. When antibodies reach 20% the epidemic stops, in many places not just NY.

To add to this, Sweden isn't seeing the big surge that France and Spain are seeing (among others, including Belgium and the Netherlands, both at or near record highs). Sweden's cases have dropped lower and have stayed there. Given their comparatively open approach to the virus, they should be seeing a surge. While it's possible it'll show up in the near future as it again spreads across parts of Europe, I think it's also plausible they've reached a partial herd immunity. The commonly repeated premise that you need ~60% to reach herd immunity is plainly false, that's a calculation meant for a vacuum. In reality people aren't numbers on a sheet or living in a vacuum, all people don't behave the same way, don't spread a virus the same way, aren't all similarly at risk, some large percentage of the population may already have immunity thanks to prior exposure to other coronaviruses, and so on.

The 60 percent figure is people living their lives normally. Currently most people are social distancing, wearing masks and large gatherings have been cancelled. Under these circumstances 20 percent may well be herd immunity. But if Madison square garden was open and the subway was packed with people not wearing masks, its not clear that 20 percent would be enough.

That seems plausible. Both New York and New Jersey have lots of high density areas, yet their numbers are very flat now. There's also some speculation that some people might have a natural immunity.

It likely happened in Florida and Texas too. Their profile basically matches New York.

I'm one of those who tested positive for IgG antibodies in April. Same in June, August. These were Mount Sinai's quantitative research tests, with a high titer. I donated plasma twice. The only symptoms occurred in mid March. Then I got an Abbott qualitative IgG test earlier this month, because I was about to fly to Italy. Still positive. Once there, to end quarantine before the customary two weeks, I got two negative swabs and another Abbott test, but this time they also tested IgM (short term response), which quite surprisingly still came back positive. Since this was the first time it ever got checked, it's not clear if I was IgM positive for the entire six months or I got some exposure in August or early September that didn't result in symptoms or infection.

I don't know what this means or if I'm just a rare case, but my inkling is still to explain NYC's current rates with mask wearing and reduced indoor interactions. I guess we'll see in the next four to six weeks.

> my inkling is still to explain NYC's current rates with mask wearing and reduced indoor interactions

Stockholm, Sweden has better numbers than New York yet people don't wear masks here nor are stuff closed. So you can't really say for sure that New York's numbers are thanks to those.

I don't know how to compare and control for different population mobility between the two or any other pair of cities in the world, which is why I mentioned that we'll see in a few weeks, i.e. comparing NYC to itself.

That might explain it--this is just a baseline level of spread and herd immunity knocks it down. It also begs the question of how to loosen restrictions because if NYC actually hit herd immunity for the current level of social interaction, not relaxing restrictions is unethical. You can't keep everything closed forever, and if there's a sign you've hit herd immunity, 3+ months of this is it. It might also be what spread looks like post-vaccine. How to know you're at that point where you can reopen is tricky.

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