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Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

medrxiv.org

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Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#31

Post by mchusma »

umvi wrote: post #2

So, according to this paper 34.2-47.5% of US citizens need immunity before the pandemic can be declared over? So best case scenario we can achieve herd immunity with roughly 100M infections/recovered. USA is currently at ~8M infections/recovered, so that means we are roughly 8% of the way to herd immunity (best case). At the current rate of +50K infections per day, that's 20 days per 1M infections, so we need 20 days…

16% is a good estimate of US infection rate.

https://covid19-projections.com/ (Excellent source during these times. Sad to see them deciding to stop moving forward but it's good for now).

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#32

Post by nradov »

These models are fundamentally flawed in that they assume immunity or susceptibility are binary conditions. Based on recent research it appears a significant fraction of the population has at least limited immunity from prior exposure to other coronaviruses. They can still get infected but the immune system clears it more quickly and they tend to suffer fewer symptoms compared to immunologically naive patients.

https://www.jci.org/articles/view/143380

https://pubmed.ncbi.nlm.nih.gov/32978311/

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#33

Post by jacquesm »

jupp0r wrote: post #15

Keep in mind that "herd immunity" isn't really immunity, it's the point at which Rt (the average number of people each infected person passes the infection on to) drops below 1.0 and the spread shrinks instead of growing. Rt is dependent on how people behave. When behavior changes, Rt can change as well. Each herd immunity level is thus dependent on health measures, which is why "reaching" herd immunity and then loos…

> R0, which is a constant inherent to the virus strain

I think you just devalued your argument.

https://wwwnc.cdc.gov/eid/article/25/1/17-1901_article

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#34

Post by jupp0r »

timr wrote: post #20
jupp0r wrote: post #15

Keep in mind that "herd immunity" isn't really immunity, it's the point at which Rt (the average number of people each infected person passes the infection on to) drops below 1.0 and the spread shrinks instead of growing. Rt is dependent on how people behave. When behavior changes, Rt can change as well. Each herd immunity level is thus dependent on health measures, which is why "reaching" herd immunity and then loos…

R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. Rt is simply notation of an estimate of R0 at a particular time. Either way, you're correct that "herd immunity", as used here, means the point at which time the infection rate begins to decline, and this is conditional on population behaviors. If people mix more fre…

> R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors.

From Wikipedia: In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted {\displaystyle R_{0}}R_{0} (pronounced R nought or R zero),[20] of an infection can be thought of as the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection.

https://en.wikipedia.org/wiki/Basic_reproduction_number

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#35

Post by timr »

Gabriela Gomes was one of the first epidemiologists making this observation (as far back as May), and has found even lower thresholds (10-20%):

https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v...

https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v...

https://www.medrxiv.org/content/10.1101/2020.09.26.20202267v...

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#36

Post by zests »

I appreciate this paper because I feel like every single article about "herd immunity" completely misses the mark and makes some rather poor assumptions. These assumptions are likely made because they make COVID seem like a bigger deal which sells more papers and gets more clicks.

When an article discussing herd immunity assumes a completely homogeneous population I just shake my head and wonder how in the world this article got published.

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#37

Post by learc83 »

StevePerkins wrote: post #11
seanalltogether wrote: post #7

Earlier quoted context omitted.

I thought I remembered reading early on that icelandic testing was showing that 50% of all people infected there showed no symptoms. Then add on how many people show symptoms but its not severe enough to get tested.

Well, then add on the number of people who just don't get a test regardless. My child had a fever a few weeks ago, it was an ORDEAL finding a place to get him tested. You have to be quite motivated. If you're not sick enough to require hospitalization, and especially if you're un-insured and poor and don't want to pay a couple-hundred bucks out of pocket, then you'll probably just ride it out and never get tested. I'…

>My child had a fever a few weeks ago, it was an ORDEAL finding a place to get him tested. You have to be quite motivated.

That's because the test won't change anything. If it's positive, they'll tell you to isolate your kid. If it's negative, there's a high enough false negative rate that you'll still need to basically treat them like they have COVID (stay home and isolate).

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#38

Post by timr »

jupp0r wrote: post #34
timr wrote: post #20

Earlier quoted context omitted.

R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. Rt is simply notation of an estimate of R0 at a particular time. Either way, you're correct that "herd immunity", as used here, means the point at which time the infection rate begins to decline, and this is conditional on population behaviors. If people mix more fre…

> R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. From Wikipedia: In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted {\displaystyle R_{0}}R_{0} (pronounced R nought or R zero),[20] of an infection can be thoug…

You can think of it that way, but we never know, in practice, what level of actual immunity exists in a population.

In any case, it's not relevant to my point: R0 is a contextual number, always defined by empirical data. It's not a fixed feature of the virus.

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#39

Post by bigbubba »

jackpeterfletch wrote: post #30
umvi wrote: post #2

So, according to this paper 34.2-47.5% of US citizens need immunity before the pandemic can be declared over? So best case scenario we can achieve herd immunity with roughly 100M infections/recovered. USA is currently at ~8M infections/recovered, so that means we are roughly 8% of the way to herd immunity (best case). At the current rate of +50K infections per day, that's 20 days per 1M infections, so we need 20 days…

This is fag packet math, so I'll spare any exact figures. But if the second wave data for the UK is anything to go by, confirmed cases vs actual cases was at _least_ 5x for the first wave. There obivously are other factors, but with increased testing that multiplier only climbs, bringing herd immunity numbers actually within reasonable grasp. I strongly suspect there have been similar effects in the US.

(People scribble on cigarette packages? Aren't those waxed cardboard or something? I wouldn't expect a pen to work well on those.)

Re: Updating Herd Immunity Models for the US: Implications for the Covid-19 Response

#40

Post by jacquesm »

timr wrote: post #38
jupp0r wrote: post #34

Earlier quoted context omitted.

> R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors. From Wikipedia: In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted {\displaystyle R_{0}}R_{0} (pronounced R nought or R zero),[20] of an infection can be thoug…

You can think of it that way, but we never know, in practice, what level of actual immunity exists in a population. In any case, it's not relevant to my point: R0 is a contextual number, always defined by empirical data. It's not a fixed feature of the virus.

Exactly. OP is simply wrong about this.
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