
Coronavirus May ‘Reactivate’ in Cured Patients, Korean CDC Says - sci_prog
https://www.bloomberg.com/news/articles/2020-04-09/coronavirus-may-reactivate-in-cured-patients-korean-cdc-says
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nil-sec
This came up since the beginning in January. The number of people that were
reported to reinfect like this seem to lie well within the expected rate of
false positives. I don’t understand how this claim is made repeatedly, without
a thorough statistical analysis of what is expected.

~~~
yread
It's not just tests. All symptoms disappear - we had health workers coming
back to hospital and days later symptoms reappeared

EDIT: to clarify: in my hospital there were colleagues who tested positive,
isolated, had no symptoms, went back to work, still no symptoms. After a few
days symptoms are back and they tested positive again

~~~
radicalbyte
It's flu season, it's quite possible they have had both flu and Coronavirus.
My wife had the flu in Feb & early March and the symptoms are identical to the
Coronavirus.

They're working in a hospital so they'll catch everything.

~~~
agumonkey
Stupid question does being infected with some virus helps if a second pathogen
infects you ? As in 'immune system globally more active' or not at all ?

~~~
hcknwscommenter
Not a stupid question, but pretty much not at all. In fact, you are slightly
immune compromised by the first pathogen against the second pathogen because
your adaptive immune system is highly active against the first pathogen. The
body has two systems, an innate immune system that has mechanisms to innately
attack bacterial and viral pathogens in general and an adaptive immune system
that adapts to each specific pathogen. The innate system is a first line of
defense but is like a form of combined suicide bomber and cannon fodder
throwing cell after cell to overwhelm the pathogen with death and there is
significant collateral damage. The adaptive immune system takes time to ramp
up to each new pathogen and if it's working on one pathogen doesn't really
switch to working on the other. Rather older cells are/have adapted to the
first pathogen and newly born cells begin to work on adapting a defense to the
new pathogen. This takes time and there are, at the beginning, very few cells
adapting to the new pathogen.

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9nGQluzmnq3M
I wouldn't read too much into this yet. Coronavirus tests are notoriously
flaky and Korea has thousands of recovered people, so it's entirely possible
that people either get false negatives twice (so they appear cured but
aren't), or get true negatives followed by a false positive later (so they
appear sick but aren't).

If there are patients who test negative for several weeks but _then_ relapse
and get clinically sick with COVID-19, we'll have cause to worry. On the other
hand, if this was a common phenomenon, it'd be happening in China already.

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rjzzleep
Whether the tests are flaky or not, we shouldn't really discard the fact that
virologists don't generally say that infected people do not get reinfected,
but rather that infected people will have milder symptoms and therefore less
lethal diseases. There was a really good episode on the immune system on TWIV
recently.

[https://www.microbe.tv/twiv/twiv-597/](https://www.microbe.tv/twiv/twiv-597/)

~~~
LordHumungous
Will COVID-19 become another cold? Were the 4 other coronaviruses that cause
colds just as deadly when they first appeared? Interesting to ponder.

~~~
bobosha
Actually yes. The virus that caused the 1918 "Spanish flu" is now one of the
seasonal flu viruses that afflict us every year.

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sci_prog
I'm hoping it's just bad tests in the first place.

[https://covid19usa.io/](https://covid19usa.io/)

Edit: Adding my website for tracking coronavirus cases over time in USA state
and counties. Original Show HN here:
[https://news.ycombinator.com/item?id=22778152](https://news.ycombinator.com/item?id=22778152)

~~~
Fragoel2
Most likely. You need to develop antibodies to defeat a viral infection and,
once you do, they don't just disappear overnight.

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hutzlibu
Well, as far as I know, the antibodies do disappear at some point, but now
your immune system knows the virus and can quickly produce new antibodies
again, if it finds the virus again. But I think over time the immune system
also forgets.

But to the patients that got sick again. "Bad test" would be the best outcome
yes, but I know, that with herpes virus for example, you can never really get
rid of them. Your immune system defeats them, but some virus cells remain in
stasis somewhere sleeping - and resurface, if your stress level is high
enough. So it would not surprise me, if this coronavirus might have similar
traits.

[https://en.wikipedia.org/wiki/Herpes_simplex](https://en.wikipedia.org/wiki/Herpes_simplex)

~~~
incompatible
Something I read recently is that the immune system is complex containing both
an innate immune system an adaptive immune system. It's possible that in mild
cases of Covid-19, it may be successfully handled by the innate immune system,
which doesn't confer additional immunity. A mild case my occur if the initial
infection is by a relatively small number of virus particles.

~~~
hutzlibu
Also possible yes. The killer cells (do not know the proper english name) are
general purpose defense cells against anything that the body does not know.
Only if there are too many unkown cells of similar type, they get categorized
by other cells in the lymphs of the immune system and then other cells finally
produce antibodies. But that process takes time.

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frank2
>The big "eating" cells (do not know the proper english name)

macrophage

~~~
imagine99
>macrophage

That's arguably Greek ;-)

~~~
teddyh
_The problem with defending the purity of the English language is that English
is about as pure as a cribhouse whore. We don 't just borrow words; on
occasion, English has pursued other languages down alleyways to beat them
unconscious and rifle their pockets for new vocabulary._

— James Davis Nicoll

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gnicholas
> _About 51 patients classed as having been cured in South Korea have tested
> positive again_

So does this mean they're symptomatic again, or just testing positive?

~~~
gwd
A friend of mine fell ill with COVID-like symptoms; bad enough to be unable to
work remotely, but not bad enough to go to the hospital and be tested (in the
UK). He was sick for 5-6 days, then felt better, and thought he'd completely
recovered. One week later, his symptoms returned for 2 days, and now he's
feeling better again.

Was it COVID the first time? Was it COVID the second time? Was it stress, or
his body adjusting to being in the same environment 24/7 (rather than spending
half his day outside the home)? We may never know. An antibody test would show
if he'd had it _at least_ once, but that could well have been 2 back-to-back
colds with asymptomatic SARS-CoV-2.

~~~
agumonkey
I Wonder if a virus could create waves inside one's body

~~~
gus_massa
It is a totally unrelated virus, but if you get chickenpox you may get many
years later shingles, the virus may remain inactive in nerve cells fo a long
time.
[https://en.wikipedia.org/wiki/Shingles](https://en.wikipedia.org/wiki/Shingles)

~~~
agumonkey
What a strange game of life

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graposaymaname
Is it me or are Bloomberg articles in general panic stricken? I've been
observing this over a number of articles lately, almost all of them are
adjusted to sound like they want us to be more afraid and tensed, maybe my
subconscious bias dunno.

~~~
hexl
I remember a thread about their writers being rewarded when moving the market.

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9nGQluzmnq3M
[https://outline.com/n8cTuW](https://outline.com/n8cTuW)

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skwb
IMHO I'm fairly skeptical of these claims. There have been a lot of scrambling
to get testing online worldwide, so I'm fairly certain that Pr(False Positive)
and Pr(False Negative) are reasonably high given circumstances. I don't have
the numbers on me right now, but I _think_ sensitivity is only 70%... So it's
not hard to imagine a situation where a combination.

The thing that in my mind sorta kills this "reinfection" argument is our
previous experience with SARS virus [1]. Figure 1 of the paper shows IgG
reactivity for up to 3 years. Anecdotally, I've heard from my immunity
bioinformatics colleagues that the spike protein that is recognized by the
immune system is very well conserved.

I haven't seen a ton of _great_ evidence that have really pushed my priors
against the conclusion that these handful of cases are better explained
somehow by faulty testing/some other combination of complication. As always,
willing to adjust these priors if given compelling evidence. :)

[1]
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851497/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851497/)

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unsrsly
It is unclear whether these patients are shedding viral RNA particles from
their prior infection or actual infectious virus from an ongoing infection.
The way to tell the difference would be to perform viral cultures instead of
the PCR-based test.

~~~
hcknwscommenter
Your post makes little sense to me. viral RNA particles are virus no? You
distinguish between viral RNA particles and "actual infectious virus". What is
the difference between the two?

~~~
usrusr
PCR tests will still detect signature bits of RNA even when the virus is
physically broken and no danger at all. Virions are not alive like bacteria
are, but they are still more than the pure RNA ("data"). To be infective they
need the whole, intact package of RNA and a set of tooling molecules that the
parent cell created created alongside the RNA copy (or that were taken from
regular cell stocks).

In year 2000 computer terms, the virus doesn't just need the bytes of the VBS
file, it also needs the email header that says "ILOVEYOU".

~~~
hcknwscommenter
Not really though. Naked RNA is incredibly unstable when just out in the
environment or floating around in blood, mucus, etc. Sure, if you dump a pot
of naked RNA on the floor, mop it up and analyze it that second your PCR test
will pick it up, but you would have to be right quick about it.

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rajnathani
I am not sure whether this has to do with testing accuracy, however we had a
similar case [0] recently in India.

> A 60-year-old woman from Pune who tested negative for coronavirus died three
> days after being discharged.

> However, on April 4, she was rushed to Sassoon Hospital in Pune, where she
> died even before admission. When her sample was tested again, it turned out
> to be positive.

[0] [https://economictimes.indiatimes.com/news/politics-and-
natio...](https://economictimes.indiatimes.com/news/politics-and-nation/pune-
womans-death-due-to-covid-19-puzzles-authorities/articleshow/75003417.cms)

~~~
rajnathani
Correction: This isn’t a case of reinfection/reactivation as the woman in
context was never tested positive when she was alive.

