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tghw | 5 years ago

NYC had only 20% prevalence in mid-June[1], after they had contained the initial outbreak[2]. Therefore, the drop in new cases is very unlikely to be from herd immunity, which would need prevalence to be in the 80% range.

The author seems to ignore that most people are interacting with far fewer people because they are working from home, kids mostly aren't in school, and our other interactions with people outside our household have been limited and altered to decrease the chances of transmission.

It's nice to think that some people had memory T-cells that could deal with the virus, and it seems some people do, but based on the original R0 numbers, it would be foolish to think that is the case for enough of the population to conclude that we've reached herd immunity.

[1] https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/comm...

[2] https://coronavirus.jhu.edu/data/new-cases-50-states/new-yor...

discuss

order

rdtwo|5 years ago

The theory was that some large percentage of population is either immune or at least significantly more resistant to covid. Do once the initial 20% get it the other 50-% are resistant so you get your 70% number that way

tghw|5 years ago

Barring concrete evidence that is the case, it's a very dangerous assertion to make. It would also mean that the transmissibility of SARS-CoV-2 is much higher than we originally thought, amongst those without "natural immunity".

Even if it were the case that half the population was naturally immune, we would want to understand why. The leading explanation at the moment is T-cells and previous exposure to other coronaviruses. Problem is, there's a good chance that previous exposures would be less likely in certain populations, like children, which could be especially problematic as we're debating sending kids back to school.

At the very least, we need more data on T-cell prevalence/reactance to SARS-CoV-2 before we can jump to the conclusion that people are already immune.

But right now, it's far more likely that we've seen drops because of the drastic measures that have been taken and the changes in daily behavior across the population.

tghw|5 years ago

Also, the JHU map is a poor indicator, as they are clearly basing the colors on suspect data, as in this case in Nebraska, which apparently had negative new cases yesterday.

[1] https://www.dropbox.com/s/uakm0cfgn2hv94r/Nebraska.png?dl=0

gloriosoc|5 years ago

Oh sometimes that happens because states make mistakes in reporting and want to correct them. I would guess that's the case here. It also happens in the other direction- big spikes are sometimes a backlog of cases all reported at once.

avremel|5 years ago

This article in the Atlantic mentions possible herd immunity at < 40%.

https://www.theatlantic.com/health/archive/2020/07/herd-immu...

tghw|5 years ago

> Back in February, Lipsitch gave a very rough estimate that, absent intervention, herd immunity might happen after 40 to 70 percent of the population had been infected.

Which is actually a mischaracterization of what the previous article[1] said:

> Lipsitch predicts that within the coming year, some 40 to 70 percent of people around the world will be infected with the virus that causes COVID-19.

At no point does he mention herd immunity. So, no, he's not saying herd immunity at 40%.

[1] https://www.theatlantic.com/health/archive/2020/02/covid-vac...

newen|5 years ago

It's very hard to trust these low prevalance numbers when, for example, I know a few people who are close friends with people in medical fields who tested positive but they themselves didn't get tested but had mild symptoms. I myself had mild symptoms that I'm 99% sure is covid and didn't get tested.

tghw|5 years ago

Just because you and your friends weren't tested, doesn't mean the statistics are invalid. The link above was from random antibody testing and has a high confidence interval.

I've been sick twice during this time. Thought it had to be COVID, but two PCR tests and an antibody test all came back negative. Maybe the tests are flawed, sure, but it's far more likely I just had something else.