Updating Herd Immunity Models for the US: Implications for the Covid-19 Response • Hacker News Board

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

#11

Post by StevePerkins » Thu, Oct 08, 2020, 3:02 PM UTC

seanalltogether wrote: post #7

zwischenzug wrote: post #5

Earlier quoted context omitted.

Actual infection count is probably far higher than 8M, isn't it? That's just number of positive tests.

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'm sure this is the state of things for tens of millions of Americans.

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

#12

Post by timr » Thu, Oct 08, 2020, 3:02 PM UTC

zwischenzug wrote: post #5

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…

Actual infection count is probably far higher than 8M, isn't it? That's just number of positive tests.

Yes. The actual number, per the CDC, is probably 5-10x higher than the current confirmed infection count.

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

(fyi: they bury the lede on this page: you have to click through to their horribly slow interactive viewer widget to see the multiples.)

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

#13

Post by cma » Thu, Oct 08, 2020, 3:05 PM UTC

zwischenzug wrote: post #5

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…

Actual infection count is probably far higher than 8M, isn't it? That's just number of positive tests.

Based on New York seropositivity, there would be a 5-6X multiplier on cases I believe. However that could change since they were test constrained when generating lots of those cases (downward?), and demographics of infected have changed (upward? younger may push multiplier higher as they are more asymptomatic and potentially get tested less).

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

#14

Post by e40 » Thu, Oct 08, 2020, 3:06 PM UTC

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…

I wonder if this also means that only 35% of us need a vaccination to declare it over. I had previously read 60-70% were needed and that 35% of Americans get a flu shot. That depressed me.

EDIT: seriously, downvoting this comment? Can't imagine why and would like to know.

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

#15

Post by jupp0r » Thu, Oct 08, 2020, 3:07 PM UTC

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 loosening up health measures won't work.

Edit: removed wrong information on R0 that's not really essential to my point

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

#16

Post by StevePerkins » Thu, Oct 08, 2020, 3:07 PM UTC

HarryHirsch wrote: post #10

StevePerkins wrote: post #6

Earlier quoted context omitted.

> USA is currently at ~8M infections/recovered CONFIRMED cases. The total number of cases is probably 5-10x that. I live in the Deep South, and honestly I suspect that our curves have fallen simply due to a "limited" herd immunity effect (i.e. the groups of people most likely to catch COVID have already done so in large enough numbers). I certainly haven't observed any significant change in behaviors since the July p…

We know that coronaplague spreads through superspreading events, person-to-person transmission is wildly variable, most people don't infect anyone, but some give it to a dozen. You'd like to know if people are wearing masks at church or if family get-togethers are now outdoors.

I think the common perception on HN, Reddit, etc is that COVID spread in the U.S. is primary a matter of conservative people flouting its seriousness. I understand the satisfying appeal of that picture.

However, I'm looking at my local health department's ZIP-code-by-ZIP-code infection map of the metro area. And it seems almost entirely correlated with poverty, not privilege. Infection spread seems mostly due to "essential" workers continuing to work. That's a problematic thing to point out, because I don't think we can or will solve for that. But it's plain as day.

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

#17

Post by beervirus » Thu, Oct 08, 2020, 3:08 PM UTC

eternalban wrote: post #9

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…

> infections/recovered This is a false binary state space. The implication here is that having "tested positive" is equivalent to having an "infection". An infection, by definition, is an alteration of the biological state of the entity with observable side-effects (symptoms). It is patently false to assert that "testing positive" for this virus is 100% indicative of an "infection". Further, "100M infections/recovere…

No, that is not the definition of “infected.”

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

#18

Post by hammock » Thu, Oct 08, 2020, 3:08 PM UTC

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…

Well, we could get to 2MM faster if we opened everything up for the less-vulnerable populations (i.e. everyone under 50 without obesity or heart conditions) for whom the survival rate is above 99.99%. You might then be looking at 500k a day rather than 50k.

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

#19

Post by ardy42 » Thu, Oct 08, 2020, 3:08 PM UTC

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…

> At the current rate of +50K infections per day, that's 20 days per 1M infections, so we need 20 days * 92 = 5 years before we achieve herd immunity (best case, assuming no vaccines)? That doesn't seem right.

I can't remember exactly where I heard it, but I believe robust herd immunity in human populations has never been achieved for a virus like this without the widespread use of a vaccine. Which makes sense, because there's evolutionary pressure on viruses to adapt, and so many diseases remained endemic and common until vaccines where introduced for them.

Edit: in response to the dead reply: the Spanish Flu didn't disappear. It killed tens of millions (out of a much smaller world population) and persisted for decades as a seasonal flu. IIRC, it didn't get eclipsed by other strains until the 50s.

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

#20

Post by timr » Thu, Oct 08, 2020, 3:12 PM UTC

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 freely, the estimate changes.

However, the observation that people don't mix uniformly still applies, even if they mix a bit more than they do now. To put it in a CS context, it's like debating the magnitude of the constant, when the algorithm has a fundamentally different asymptotic behavior.