[MereInterest]

Exactly. Absent a vaccine, herd immunity is the failure condition that occurs when a virus has infected as many people as it can within a population. It is the default baseline against which all interventions should be compared.

[claudeganon]

If immunity to the disease is not long-lasting (> 3 months), herd immunity is likely impossible. There are plenty of viruses that can reinfect people who have recovered from them (Coronaviruses being a common example of these) for which we have no herd immunity.

[abainbridge]

Is there any evidence you can re-contract Covid-19? If not, I'd fall back to the following argument: Some health care workers have been exposed regularly for six months by now. It'd be very news worthy if someone was confirmed to be re-infected. Given I haven't seen that news, I think I can conclude that immunity lasts at least six months in working age people.

Also, if I understand correctly, it has recently been shown that people who were infected with SARS 17 years ago still have memory T cells for SARS. (And, I think SARS is one of the viruses most closely related to Covid-19, and therefore there's reason to expect a long immunity period for it too).

"Memory T cells induced by previous pathogens can shape the susceptibility to, and clinical severity of, subsequent infections. <snip> We then showed that SARS-recovered patients (n=23) still possess long-lasting memory T cells reactive to SARS-NP 17 years after the 2003 outbreak." - from https://www.nature.com/articles/s41586-020-2550-z

[claudeganon]

There’s initial evidence of reinfection and limited immunity that are under further investigation:

https://www.vox.com/2020/7/12/21321653/getting-covid-19-twic...

https://www.theguardian.com/world/2020/jul/12/immunity-to-co...

[__blockcipher__]

There is no credible evidence of re-infection. The isolated cases can be explained away in a bayesian sense by PCR false positives or false negatives. It’s the usual base rate neglect fallacy.

The idea of reinfection contradicts decades of well established immunological principles. It also ignores the fact that we have a close relative of SARS-2 to study. That relative is SARS-1 and we have detected strong t cell activation after 17+ years. Therefore immunity is enduring and long lasting.

SARS-2 is substantially structurally similar to SARS-1.

Alternatively, take a statistical argument. There have been millions of cases around the world. SARS-2 is highly infectious for those who are susceptible. Therefore we would have thousands if not more well-documented, inarguable cases of reinfection. We don’t have those. All we have is a bunch of articles from heavily biased sources like Vox that have a vested interest in pushing the “doomer” narrative.

Why haven’t we seen widespread reinfection if it is truly possible?

[claudeganon]

As I pointed out downthread, there's a Kings College study under review that says antibodies seems to wane rapidly:

https://www.sfchronicle.com/health/article/With-coronavirus-...

https://www.medrxiv.org/content/10.1101/2020.07.09.20148429v....

Likewise, asymptomatic cases appear to have limited immune duration and development:

https://www.jci.org/articles/view/138759#ABS

And meaningful immunity might depend on how much of the virus one is exposed to:

https://www.nature.com/articles/s41591-020-0965-6

If this research holds up, we'll have your well documented cases in probably 3-6 months. Frontline doctors, outside the one cited in the Vox article, are already insisting its true.

[__blockcipher__]

Antibodies do wane, and they are supposed to. They generally don't last longer than a few months with SARS-[1,2].

Even though they wane, memory b cells persist, meaning subsequent infection is milder and theoretically less transmissible.

Additionally that reinfection potential only exists if you ignore t-cells. When you factor in t-cells, it simply does not happen.

We're in July 2020. SARS-2 existed since some point in 2019, probably midway through. Granted we couldn't detect reinfection until the whole globe had been freaking out about it, so let's start our clock from January 2020.

It's been 6 months and we don't have dozens of well-documented, credible reinfections?

No, such one-off supposed reinfections are much more explainable from a bayesian perspective of either false positives or false negatives of PCR.

Find me someone who is not immunocompromised, who is PCR-positive for SARS-2 and from whom viable SARS-2 is successfully cultured, then show them fighting off the infection and being PCR-negative and symptom-free for weeks, then show me them being PCR-positive again with viable SARS-2 cultured from their body. That's the standard.

20 examples of that and reinfection definitely happens. Until then, our priors are that we should assume it does not.

Such fears are just used to argue against herd immunity, which has been made into a "dirty word" (phrase). Herd immunity is a natural phenomenom, arguing "against" it is like arguing against natural selection in my book. (The analogy is not perfect but I hope you see the point. I'm tired of being called callous for saying "hey let's not fuck with the normal population immunity dynamics that we've used for every other highly infectious virus in existence")

---

BTW, I can't find the study but they have tested reinfection in primates and showed them unable to get reinfected

[js2]

Meta: your comments on this thread imply a degree of certainty that isn't justified by the evidence as I understand it. I am just a lay person here, but that's my impression as someone who has done a lot of reading.

As far as coronaviruses go, there are four mild human coronaviruses that are responsible for about 15% of common colds and for which humans do not develop any long lasting immunity.

There are also the three severe human coronaviruses: MERS, SARS-CoV, and SARS-CoV-2. AFAIU, long-lasting immunity to these is not well understood.

I do not understand how you can make such an authoritative statement about re-infection risk based on the limited data we have about SARS-CoV-2. Here's what immunologists have to say:

> In summary, progress since January 2020 has been impressive, but there is still so much more to learn. Are T cells protective and if so which are the key antigens and and cytokine effector programs to focus on? Are all T cell responses beneficial, or are some contributory to immunopathology and to be avoided? If it is indeed the case that antibodies are transient and T cell memory is more durable (though, how durable?), what can we learn about anomalies of T follicular helper-B cell interactions in germinal centers? In the short to medium term, we need to ensure that all of this T cell toolkit and knowledge is brought to bear on robust, comparative evaluation of the different vaccine platforms, their immunogenicity, efficacy and safety. Entering the next part of the battle, there are many thousands of people suffering the chronic aftermath of infection posed by chronic, so-called ‘long-COVID’ cases, characterized by diverse symptoms including fatigue, joint pain and dyspnea (19). A more detailed understanding of the T cell immunology will be valuable in deciphering this pathogenesis.

https://immunology.sciencemag.org/content/5/49/eabd6160.full

What I read there is a lot of "we're not sure yet."

[__blockcipher__]

Of course there's uncertainty, but the idea of re-infection contradicts decades of established immunological principles.

At a minimum, we can agree that in the event of re-infection, the subsequent infection will hit a lower peak viral load and therefore theoretically a much milder outcome with reduced transmissibility, right? This is called immunological memory and arises due to memory b cells and memory t cells which persist across decades.

Anyway, please see https://www.nature.com/articles/s41586-020-2550-z

It establishes that those exposed to SARS-1, which structurally and functionally is incredibly similar to SARS-2 and thus is our best model of how to think about SARS-2, have long-lasting immunity. Their t-cells not only react to SARS-1 after 17 years, they also have immunity to SARS-2, which is a testament to how similar they are structurally speaking.

Additionally exposure to those common cold human coronaviruses you mentioned almost certainly confers immunity to SARS-2 based off that same paper. We're still hashing out the details, of course.

Immunology is incredibly complex and there is still plenty to learn about as far as the exact specifics of what unfolds here, yes. But we should assume reinfection isn't possible, because:

- It doesn't happen in SARS-1 which is by far the best model we have

- If it did happen, given the MILLIONS of cases of COVID-19 worldwide, we would have seen THOUSANDS of rigorously documented examples of the phenomenom happening

- Those arguing for reinfection tend to not make any mention of immunological memory

- Those arguing for reinfection do so to in an attempt to scare us into staying locked down until "the vaccine", which I am opposed to because I am opposed to any public health policy that banks on a future technological innovation that does not yet exist, particularly when I fear that the environment of irrational fear and anxiety and outright hysteria is going to be used to mandate vaccines, which is highly unethical under my moral framework

--

As far as me sounding over-certain, frankly it's cognitive draining to be arguing against a horde of people whose priors have been completely screwed up by programming from a media that takes delight in knowingly lying to citizens, and even our trusted public health officials like Fauci don't have the courage or perhaps the desire to break out of the collective mass delusion we are all trapped in.

So yes, if I had infinite time and energy I agree, I could do a way better job of capturing uncertainty. I've written an 8000+ word writeup on COVID that does a much better job capturing the uncertainty, but it's very difficult to do without...writing 8000 words.

Also this doesn't justify it but I do feel the need to point out that those arguing for the "doom" scenario are even more egregiously overstating certainty, and tend to not be called out on their ridiculous statements. So that's why I tend to come into these threads guns blazing, with the predictable result of getting hammered by downvotes. C'est la vie.

[gridlockd]

Immunity isn't a binary, neither is herd immunity. While there are reports of reinfection, those cases are quite rare.

Even a modest degree of immunity can significantly lower spread. In France, Spain, Germany, you still have hundreds of cases every day, but they don't grow to thousands of cases anymore.

[claudeganon]

> While there are reports of reinfection, those cases are quite rare.

The disease hasn’t been around long enough to make this claim.

> Even a modest degree of immunity can significantly lower spread. In France, Spain, Germany, you still have hundreds of cases every day, but they don't grow to thousands of cases anymore.

This is true, but depends on the duration of immunity and a more uniform global response (or very tight border and quarantine adherence). Ongoing, sporadic COVID crises would still be pretty disruptive unless we have highly effective therapeutics.

[tripletao]

Sweden has roughly 80k confirmed coronavirus cases in 10M people. Assuming equal probability of first and second infection (which I believe undercounts second infections, since some people have more opportunity for exposure than others due to their jobs and lifestyles), and assuming equal probability of first and second detection (which again I believe undercounts), we should have something around 10M*(80k/10M)^2 = 640 confirmed reinfections.

So where are they? Are you claiming that these hundreds of confirmed reinfections simply haven't been reported? Note that the number of actual reinfections would be orders of magnitude higher; the calculation above already assumes underascertainment by a factor of ~100x. You can redo this math in any moderately hard-hit region, though I chose Sweden here because their rate of infections vs. time has been more constant (eliminating the possibility that all the infections happened in a brief early peak, after which everyone acted more carefully so there's no longer any opportunity for reinfection). I'm not saying that reinfection is impossible, just that so far, if it exists, it's very rare.

And please don't cite the Vox article. In normal times, it would be criticized as "science by press release" or worse, a single anecdotal case written up as definitive for the popular press, with no case history and no publication to review. Maybe the author's patient really did get reinfected and it's common (but that seems vanishingly unlikely to me per above), or maybe the patient was reinfected but it's rare like getting chickenpox twice, or maybe the patient just had one long infection and tested false-negative (which is very common generally) in the middle. But since the author has disclosed nothing but the shocking headline result, we can't know.

So I believe you are sowing public panic without evidence. While it is impossible to directly demonstrate that immunity for a disease discovered X months ago lasts longer than X months, it is reasonable to expect that in this case. Maybe you think that at worst, if you're wrong, then you're telling a noble lie--but the public health authorities who said masks don't work (remember that?) did too, and look how that ended up. I can easily imagine Trump on television a year from now explaining that because people got reinfected, the vaccine is obviously a scam.

Abandoning the truth in favor of a perceived noble goal has unpredictable but generally bad effects, and I wish people would stop. Or if you actually believe what you're writing, I'm not sure what to say--please read the scientific literature (and not the popular media, which has been horrible in all directions), dust off your high school biology, and make your best assessment based on that. I think you'll find that while the coronavirus is a very serious problem, it's not the near-apocalyptic one that your comments seem to imply.

[claudeganon]

There's a Kings College study under review that says the same thing. Antibodies seem to wane rapidly:

https://www.sfchronicle.com/health/article/With-coronavirus-...

https://www.medrxiv.org/content/10.1101/2020.07.09.20148429v...

Likewise, asymptomatic cases appear to have limited immune duration and development:

https://www.jci.org/articles/view/138759#ABS

And meaningful immunity might depend on how much of the virus one is exposed to:

https://www.nature.com/articles/s41591-020-0965-6

I linked to the Vox article because it covers a lot of bases in disputing the spurious narratives that have circulated in places like the US, where the disease is out of control, pandemic response is poor, and various forms of denialism are used to excuse all of this. I don't think its an apocalyptic scenario for humanity writ large, but certainly a dangerous one for many countries, especially if an ongoing, effective public health response is required.

>While it is impossible to directly demonstrate that immunity for a disease discovered X months ago lasts longer than X months, it is reasonable to expect that in this case.

Instead of attributing motives to other people, perhaps interrogate your own need to insist on statements like this, absent any evidence, as well as the tone of your broader rebuttal. I have no intention of sowing panic or engaging in "noble lies," but nor will I embrace evidence-free narratives to soothe myself or others.

If the US intervened early or effectively with measures like those in Taiwan or South Korea, we would likely have the situation under control. It's still possible that we could do this and I hope that we do.

[tripletao]

I appreciate the reply, and I agree that the concentration of antibodies in the blood has been observed to drop with time. That's relatively common in many diseases though, and doesn't mean that the patients no longer have any useful immunity. The test thresholds were set for best (but still imperfect) discrimination between known positives (mostly severe cases) and known negatives, and there's no specific reason to believe they predict when a recovered patient becomes susceptible again. They're also testing for IgG, when we know that T cell and IgA immunity are important. One of your papers mentioned IgM, which is expected to drop quickly to undetectable levels while the patients retain immunity (not to say you suggested otherwise, of course).

I also agree that whatever immunity patients get after a mild or asymptomatic case is likely to be weaker than after a severe case. That's one case where my calculation above could be wrong--if there are many reinfections but the first or second case is always very mild, we might be much more likely to miss those. That would still be good news for the patients, though bad news for the overall population if they're still comparably infectious.

Finally, even if a patient's immunity degrades to the point they no longer exhibit sterilizing immunity (i.e., the virus still replicates a little at first), in most diseases they won't get as sick as the first time. So even if the coronavirus becomes endemic (which seems relatively likely, since many countries will lack the resources to eradicate it even with a vaccine), I expect the cost in mortality from whatever reinfections do occur to be far lower than what we're seeing now. The opposite of that (antibody-dependent enhancement) does occur, and was a specific concern here because vaccine studies for the original SARS showed evidence of that. So far vaccine studies for SARS-CoV-2 do not, though.

I actually thought the SF Chronicle article wasn't terrible, more pessimistic in its conclusions and tone than I would be given the same evidence but with many of the points above. Their headline seems irresponsible to me though; even if durable sterilizing immunity were impossible, a vaccine that cut the IFR by a factor of ten would be tremendously valuable to the elderly. All that nuance is lost when people just say "reinfection is possible". I was probably too strong to say "sowing public panic", but I do believe your comments paint a falsely pessimistic picture of the current science, and that this false pessimism can be harmful later (e.g., by causing people not to seek a vaccine because of something they half-understood about immunity). Specifically, I also believe the absence of confirmed reinfections out of places like Sweden is strong evidence that immunity usually lasts >3 months. If you were claiming that reinfection might be common after a year, then I'd be much less sure (though I'd still guess probably not based on the original SARS).

In any case, I certainly agree that younger people shouldn't get themselves deliberately infected in search of whatever immunity that affords (though the death rate among young people is low enough that I doubt reinfection would change the calculus for anyone considering that either way). I also agree that the USA response has been terrible, and resulted in a lot of avoidable death--I'm not sure, but it seems possible to me that just with universal mask use and good hygiene (like in Japan), we could live otherwise normal life with negligible spread.

ETA: And here's a paper showing neutralizing antibodies for at least three months (the limit of the study, which they're continuing) in New York. It seems beyond any reasonable doubt to me that immunity lasts three months, and I believe you're simply wrong to question that. Longer gets more speculative, but I think it's quite likely.

https://www.medrxiv.org/content/10.1101/2020.07.14.20151126v...