
Herd Immunity - EndXA
https://en.wikipedia.org/wiki/Herd_immunity
======
OliverJones
Reading the simple formulas in this article, it looks like the present
strategy of "social distancing" is intended to reduce R(0), the number of
persons infected by each infected person. Pretty obvious, but still it's good
to have a clear understanding.

It would be good if the same strategy could somehow be applied to the person-
to-person spread of misinformation. But that's harder, witness some of the
comments here.

~~~
microcolonel
> _person-to-person spread of misinformation_

You know, for as much as I've heard about the supposed danger of
"misinformation", so many factual observations have been labeled
"misinformation" early on, only to be later confirmed by WHO, a major national
authority, or a medical journal.

The type of misinformation matters a lot, because if people take the concerns
about permanent lung damage, reproductive damage, and the extreme
contagiousness of the virus seriously, it doesn't matter if they were
"misinformed" to some extent. If the misinformation encourages them to not
take things seriously, or to breach social distancing (see Rudy Gobert, who
should hope he hasn't committed homicide for a laugh), that's when it is the
most dangerous.

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dmos62
There's been talk that previous coronaviruses don't cause immunity and there
already seems to have been cases with this one where a person got it twice.
Does anyone have insight?

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hirundo
I've read that coronavirus is a near relation to the common cold virus. How
significant is it that catching a cold doesn't seem to give you immunity from
catching another?

~~~
na85
That's because the common cold mutates very quickly, so by the time you catch
another cold it's effectively a new virus.

~~~
hirundo
Is coronavirus different in that respect?

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AstralStorm
If we can use data related to Human Coronavirus strains (HCov), which are
responsible for many colds, then not that much different.

Of course, SARS-CoV-2 could be different. For SARS-CoV and MERS-CoV, there was
no data on this.

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grey-area
This is the best solution we can hope for now with Coronavirus IMO.

Slow the infection rate (but not too much) till we hit enough cases to have
herd immunity, which will then slow the rate significantly till it mostly dies
out (I suspect this has happened in China and South Korea, if not they will
suffer the consequences later as the virus is reintroduced unnoticed from
another country).

Since it won't be stamped out worldwide this year, there's no point in
attempting complete eradication and tracing all contacts. That means the aim
of reducing the spread should not be to avoid infections, but to to reach herd
immunity in an ordered way without taxing healthcare systems too much on the
way.

~~~
mathdev
> I suspect this has happened in China and South Korea

How could it have if only a negligible fraction of the population caught it?

~~~
empath75
Do we know how many people are already susceptible to it? It’s plausible that
some percentage of people are immune to it already — maybe they recently
caught a similar coronavirus or some other natural resistance to it.

~~~
ibejoeb
Something seems a little off. If this thing truly incubates for up to 14 days,
during which time it can be transmitted, it seems odd that so few people are
ill.

Is it possible that many people, in fact, are infected but do not get sick?

~~~
AstralStorm
It is likely that the early symptoms get ignored, as they are similar to a
cold - except the nasal discharge and phlegm, which SARS-CoV-2 does not seem
to cause. (It gives dry cough instead of wet cough.)

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empath75
To be clear, a strategy of allowing this to spread unchecked will result in
10s of millions of people dying around the world.

~~~
randomsearch
If you’re referring to the UK strategy, it is not to be “unchecked”.

~~~
reidrac
I'm not sure how sound is UK's strategy.

Current advice is to self-isolate for 7 days if persistent cough suddenly
appears and/OR a temperature of 37.5°C (that is not high temperature).

That sound like good advice, but they are not going to test those cases unless
it ends in hospital. And they don't want you to call to the NHS help line or
go to the doctor (again, not bad advice but I see some people getting anxious
about this; IMHO at least the help line should be available because most
people aren't doctors).

Considering that it could be a mild case of the disease or any other common
seasonal disease (I have two toddlers at home: they get ill), how can we tell
we had passed the disease and we have some immunity?

Besides, if testing and tracing stops, it means there won't be information
about the progression of the epidemic in the UK; which sounds to me like a bad
idea (but I'm not an expert).

Considering how the Conservative government has been underfunding the public
health system for 10 yeas, I understand how their approach can be seen by some
as untrustworthy.

EDIT: I see this may be off-topic re: herd immunity, sorry about that.

~~~
randomsearch
> Besides, if testing and tracing stops, it means there won't be information
> about the progression of the epidemic in the UK;

Yes, there will. It will be inferred from hospital stats.

Testing and tracing (apparently; I'm no expert, parroting what I've read from
experts) is only useful in the contain phase. After that, you're better
focusing on slowing the spread in the delay phase.

That said, Singapore and China have shown success with testing, tracing, and
extreme measures. The assumption of the UK Government, however, is that in the
long-term these measures will fail and kill more people than following a delay
phase strategy.

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MoOmer
Early on, doctors were quick to note that there is no herd immunity with this
particular coronavirus.

~~~
dboreham
No _existing_ herd immunity. That doesn't mean "herd immunity doesn't work for
this virus" which is I suspect what you're thinking.

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therealmarv
It's currently unknown if there is an immunity after getting Corona.

~~~
jessriedel
All signs point to the coronavirus infection inducing normal immunity. The
number of apparent reinfection is extraordinarily low, consistent with being
due to testing error, and in any case not relevant even if real if it only
applies to a small fraction of the population. Furthermore, the virus does not
have a segmented genome like influenza (thought to be responsible for its
rapid evolution and ability to evade vaccine) and is a single "species"
(unlike the huge family of viruses, mostly rhinoviruses, that cause the
unvaccinable common cold).

~~~
wiremine
That's great news. Got any links to the data?

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jessriedel
I just found some strong counter evidence in tension with everything I'd been
hearing:

Francois Balloux (Computational biologist, director of UGI at UCL): "How long
immunity lasts for following covid-19 infection is the biggest unknown.
Comparison with other Coronaviridae suggests it may be relatively short-lived
(i.e. months). If this were to be confirmed, it would add to the challenge of
managing the pandemic.

[https://twitter.com/BallouxFrancois/status/12388371671426416...](https://twitter.com/BallouxFrancois/status/1238837167142641664)

It's not inconsistent per say, since it still seems that the recent
reinfections were likely due to test error or rare poor immune response, but
my initial comment is misleading enough that I retract it (and would delete it
if I could).

------
_red
An interesting side discussion to this regarding vaccines: Does the presence
of vaccine antibodies exhibit selection pressure on viruses? That is to say,
do vaccines inadvertently and indirectly create an 'arms race' scenario?

 _NOTE: I am not anti-vaccine. This is intended as a nuanced point_

~~~
coretx
In some cases it does, in some it does not. And yes, the western world taking
their flu shot does mean that those who can't afford it might have a problem
or a worse problem compared to what would otherwise be. ( Also why many
advocate you should only take it if you need it. )

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erpellan
Herd immunity until now referred to immunisation (ie vaccination). It is not
at all clear that allowing people to get infected and recover will achieve the
same result.

~~~
ComputerGuru
Herd immunity is a term describing a steady-state distribution and one avenue
(the typical one) of getting there is vaccines. Typically when 80% of the
population\\* is immune _for one reason or the other_ a population is said to
have herd immunity. The idea is statistical safety for susceptible individuals
(yes, typically those that cannot be vaccinated for $reasons) thanks to being
significantly outnumbered by those immune/resistant to infection - or a buffer
population acting as a firewall, if you will.

I haven’t seen the term used for small pox in the Modern Era, but I believe it
would be fair to say even though the small pox vaccine hadn’t been invented
(and wouldn’t be until 1796), there were definitely periods of herd immunity
in major European cities/ports of the time as it absolutely destroyed the
previously unexposed Native American population.

But when dealing with “learned immunity” due to previous exposure as compared
to natural/genetic immunity to the same diseases and the antibodies are not
passed down from mother to child, what you’re going to see is a resurgence in
cases as each new generation loses that immunity. In the present case, the
unvaccinated herd immunity would be something to keep spread in check until a
vaccinated herd immunity can take its place (assuming the vaccine isn’t
developed before 80% of the remaining population has been exposed to and has
recovered from this particular variant of the coronavirus).

\\* at least that’s the number we were taught in my livestock/farm animals
veterinary medicine class a decade ago.

~~~
erpellan
Thanks! That makes a lot of sense. Certainly more than the pundits currently
lambasting the UK health services for their strategy of flattening the curve.
The current argument against being (I kid you not) that the health authorities
are somehow stupid enough to think that immunity can be passed between
individuals like the virus itself.

I appreciate you taking the time to correct me.

~~~
ComputerGuru
No problem. I wasn’t yet aware of the UK drama when I wrote that.

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tim333
If this is going to happen and we don't get a vaccine in time one interesting
possibility is to look at stuff like hydroxychloroquine as a prophylactic that
seems pretty good in vitro and could maybe reduce the infection from very
nasty to not too bad in the appropriate dose. I'm hoping for some trial and
error research here.

paper showing it good in vitro
[https://www.ncbi.nlm.nih.gov/m/pubmed/32150618/](https://www.ncbi.nlm.nih.gov/m/pubmed/32150618/)

medcram talking about that
[https://youtu.be/vE4_LsftNKM?t=200](https://youtu.be/vE4_LsftNKM?t=200)

some semi evidence of it working in real life - the lupus patients didn't get
it in Wuhan here
[https://www.jqknews.com/news/388543-The_novel_coronavirus_pn...](https://www.jqknews.com/news/388543-The_novel_coronavirus_pneumonia_has_short_term_curative_effect_on_the_treatment_of_new_crown_pneumonia.html)

I was wondering how you could encourage people to try it and see if it works.
My idea - if you got a thousand health frontline workers to try and compared
with a similar number who didn't you may get decent data in a week or two if
lots of one group got sick and the other didn't. Or it might not work. Don't
know till you try though and could save many lives.

~~~
jonplackett
There was a lot of talk about this early on in China’s epidemic. Is there any
newer evidence anyone’s seen? Seems to have gone quiet.

I wonder if this is would be more effective in the second stage of getting
COVID-19, which is the immune system going haywire rather than the virus
directly causing problems.

~~~
tim333
There's this trial where chloroquine worked well for treatment. (4.4 days to
negative tests)
[http://news.southcn.com/nfplus/gdjktt/content/2020-03/09/con...](http://news.southcn.com/nfplus/gdjktt/content/2020-03/09/content_190536632.htm)

Tocilizumab seems good for the later stages
[http://www.ansa.it/english/news/science_tecnology/2020/03/11...](http://www.ansa.it/english/news/science_tecnology/2020/03/11/coronavirusarthritis-
drug-seems-to-work_8113f9d9-9bb8-4181-9c02-3e314c30e7e9.html)

Prophylaxis, taking the drugs before catching the virus, remains a bit
untested.

~~~
jonplackett
Thanks. The first one seems positive. I wonder why no other countries are
using it then?

(Here’s a translate link for anyone who can’t read mandarin.
[https://translate.googleusercontent.com/translate_c?depth=1&...](https://translate.googleusercontent.com/translate_c?depth=1&hl=en&nv=1&rurl=translate.google.com&sl=auto&sp=nmt4&tl=en&u=http://news.southcn.com/nfplus/gdjktt/content/2020-03/09/content_190536632.htm&usg=ALkJrhjCR7mu8Nrfx8Fhmhvx5rUIMeIjAQ))

The second one is a different drug isn’t it? An arthritis drug rather than an
anti-malarial.

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buboard
It's getting very hard to believe the UK story. I mean, i get exceptionalism,
but this is going too far.

~~~
toyg
The UK has some of the best epidemiology schools and experience, thanks to a
tradition harking back to the British Empire expanding in very dangerous
lands.

HOWEVER

Imho, precisely this wealth of experience is driving a lot of people to
overthinking it, looking too much at the long-term big picture and not
weighting the immediate costs correctly. Some people have ended up in
Strangelove territory and we risk paying a big price for it. Saving more
people right now is worth, say, a longer impact on the economy or longer
quarantine measures, if anything because those are social constructs that _can
adapt_ \- whereas our bodies work only one way.

~~~
buboard
> The UK has some of the best epidemiology schools and experience, thanks to a
> tradition harking back to the British Empire expanding in very dangerous
> lands.

This is not an argument in 2020. This is the kind of exceptionalism i m
talking about

~~~
toyg
I’m not the one saying that, Italian experts are saying it, because it
increases the level of bafflement they experience when looking at the
(non-)approach the UK is taking at the moment. I am extremely critical of this
(non-)approach, I’m just trying to figure out where it comes from and this
might well be a factor, sadly. After 2016, I’ve learnt never to underestimate
the often-misplaced sense of superiority that the English upper classes have
drilled into the wider population for the last 200 years, and the degree of
detachment of their elites.

