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Comment by kleiba | Hacker News Reader

In other words, when you recover from covid-19, you are immune to it

How does this follow?

That doesn't strictly follow.

Here is the thought process, though. Typically when you get an infection, your body builds antibodies that can attack the pathogen. The next time the pathogen shows up, your body kills it before you get sick. This immunity doesn't always last for a lifetime, but there is pretty much always some immunity. With COVID-19, early reports showed that this wasn't happening; people got sick, recovered, and then got COVID-19 again. What the news article says is that the test was wrong; when they tested positive the second time, the test was just returning incorrect results (because of limitations of the PCR technique; it's testing for certain RNA, not for the existence of an infectious live virus).

So to say that this means you can be immune to SARS-CoV-2 is not strictly correct. What it says is that there is no reason to think that this virus is any different from many of the other viruses that we already know about. (We do know about viruses that you can't be immune to, like HIV. But those viruses explicitly attack the immune system machinery that is supposed to kill them. We have no evidence that SARS-CoV-2 does that.)

We also know that immunity to coronaviruses generally declines rapidly. We have no idea how long somebody is immune to Covid-19 when they have recovered.

I think it's an overstatement. When you recover from it, you don't still have it, even if you test positive. That means that at least some of the "got it a second time" reports are false.

Are they all false? Don't know. There's hope, but not yet evidence, so far as I know.

What evidence are you using to show people have recovered who are still testing positive? What confirms that the positive test is false?

Can you provide some sources?

Is this a joke? Literally the article at the top.

No, not a joke, you seemed to be talking from a general perspective rather than "in the results in this particular PCR test in South Korea". As if you had generally applicable information.

My understanding was there were many different tests being used ... so on what basis are you making that generalised statement.

> When you recover from it, you don't still have it, even if you test positive. //

A plausible explanation for specific tests doesn't make this a universal truth; so presumably you are relying on more information? Also, there being an explanation for positive tests based on dead virus, doesn't mean all post-infection positive tests are due to dead virus; that's a massive assumption.

He is right, people may be testing positive just because of dead virus fragments, but to say they have fully recovered there must be no virus alive in their bodies - lack of symptoms may suggest it, then having antibodies may guarantee that eventually..

.. assuming the virus can not hide (and be able to leave) where they can't penetrate - like in the eye ?

.. and with weak immune system the outcome may be (how?)long undecided as the antibodies are not being able to fight the virus fast enough to finish it definitely?

> Are they all false? Don't know. There's hope, but not yet evidence, so far as I know.

You mean there's evidence but not proof.

That's how immunity against pathogens usually works. There are exceptions like the flu which mutates into sufficiently distinct strains that the immune system doesn't (fully) recognize. I'm still oversimplifying here.

Well viruses in general, AFAIK, mutate - and that's how we trace their movement through the infected: you sample the virus and look at the mutations eg https://nextstrain.org/ncov.

Do we know for sure that Covid19 in N.Europe isn't sufficiently mutated over that in Australia, say, that secondary infection is possible (even if recovered people's antibodies recognise it somewhat)?

We don't know much for sure.

What I've heard from experts in the field, but I don't have sources, is that the type of RNA virus is different from influenza and doesn't mutate as quickly - which is potentially good news for those hoping for a vaccine.

How would you recover at all if your body weren't producing antibodies capable of killing it?

It doesn't strictly follow, you're right. But this punches a huge hole in the already kind of surprising/unlikely possibility that we had suddenly just discovered the first (or if I'm wrong, "a very rare") virus that can re-infect the same person with the same strain.

In at least two ways I can think of. First, these fragments have been inactivated, probably by the immune system, suggesting you have some immunity (obviously, that's not the same as being perfectly immune). Second, given how infectious the virus is, the fact they're not finding genuine positive re-tests strongly suggests some immunity is happening.

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