It remains to be seen over the long-run whether antibody levels correlate inversely with either risk of: a) _any_ Covid infection or b) _severe_ Covid infection.
Antibody levels are often cited as prediction surrogates early on because they are easy to measure. Occurrence or recurrence of infection, irrespective of antibody levels, of course, takes time. Also remaining to be seen is the role of T-cell mediated immunity in reducing the severity of Covid infection. If that role is significant, then declining antibody levels may be less worrisome than people believe currently.
One of the issues is that we conflate "antibodies" with "immunity". Antibodies are something we can measure so that's why there's been so much emphasis on them. But they do naturally diminish over time.
Long term and durable disease immunity comes from B-cells and T-cells. They create antibodies when they run into an infection they've seen or even not seen before. Unfortunately those are difficult to measure.
Good recent podcast from Dr. Peter Attia discusses this (How B cells and T cells work together to defend against viruses [22:00])
I have been skeptical that antibodies are a good proxy for vaccine effectiveness. Your immune system "remembers" how to create antibodies, and there's no clear reason why it would continue to produce them after an infection has been eradicated. So I would expect antibody levels to always drop off naturally over time until your next exposure (or vaccine) with little or no impact on actual effectiveness, regardless of the virus or vaccine.
I mean, I suppose that also suggests that "high antibody loads" indicate your immune system is an a high-alert state against coronavirus, actively fighting the virus (or what it thinks is the virus, the vaccine) and a "low" load a less alert state, so perhaps the rapid immune response in a "high alert" state is better...but surely there is some reason our immune system doesn't remain in a high-alert state indefinitely?
[Edit - plus, of course, antibodies are far from the only immune response, they're just the easiest to measure, something that also makes me very leery of their use as a metric.]
It may also be telling us that the antibody tests and our understanding of how antibodies help in protecting against severe Covid may be wildly wrong. Vaccine data indicates overall immune response is protective, and can be successfully prompted, and that is correlated with antibody levels, but there may be more going on here.
Not the OP, but antibodies are just one part of a fairly complex immune system and it does not make too much sense to concentrate just on them. Antibodies are proteins and their level goes down over time naturally. What really interests you is the level of immune response on subsequent exposure to the pathogen, which may be pretty robust even if antibodies are low or undetectable at the moment of new exposure.
We obviously do not know yet whether we can get permanently robust immune response to SARS-CoV-2, either from vaccines or from natural infection; the virus is only two years old. We know that we can get permanently robust immune response to the viruses you mentioned in your post. But this cannot be easily generalized to any new virus that comes along.
The myopic focus on antibody levels is misplaced. We know that for Covid there are much broader forms of immune response which are not captured by antibody titers and are quite long lasting.
It's not just antibodies though. Vaccines also trigger you to get memory cells, which have a longer life span. So even if your antibody levels go down after ~6 months, and you might get infected again, your immune system will have a faster and more precise reaction, preventing a more severe course of covid.
No that's simply wrong. Antibodies are relatively unimportant and levels decline quickly. What actually matters far more is cellular immunity. Fortunately the vaccines and recovery from infection have both been shown to produce a significant level of durable cellular immunity in the vast majority of patients.
Who do you personally know in the linked podcast? What are your medical qualifications?
We already know that T-cell immunity has a major role in reducing the severity of COVID-19. There is no real question about that. Antibody levels are transient and comparatively less important.
The obsessive focus on neutralizing antibodies in blood samples is beginning to border on irresponsible.
Circulating antibodies are one facet of the layered immune system response. Mucosal membrane antibodies and T-cells (mucosal membranes have their own 'micro-immune system' which injected vaccines do little to help), general T-cells, etc are extremely important in overall immune system response. One could argue that mucosal immune system health and then T-cell response are more important than blood antibody levels.
Also general inflammation in the body, endocrine system health, and immune system modulation are important factors affecting COVID outcomes. I think there has not been near enough attention on these factors.
"Our study shows that over time there is a reduction in the proportion of people testing positive for antibodies. It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts."
As a lay person, I think it is somewhere in the middle. In all likelihood antibody presence does mean some level of immunity or at least resistance. But testing is still only measuring presence of antibodies, not their efficacy in resisting future infections. Furthermore somebody who is reinfected but has antibody driven resistance may end up behaving as an asymptomatic case.
Antibody count falls at first, but relevant antibody-producing cells were found[0] to remain in the bone marrow. I suppose it is not the only determining factor in susceptibility to symptomatic infection, though.
I’d be curious if currently available vaccines stimulate such preexisting antibody-producing bone marrow cells of past COVID patients (which sounds more optimal on the face of it), or they trigger yet another variety of antibodies to be produced in addition to the “native” one.
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.
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.
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.
Trouble is the article misses a very important point: that's just antibody (B-cell mediated) immunity. There is also T-cell immunity, which is harder to quantify so it doesn't get much attention, but we can be quite sure that it plays important role because many people who recovered from COVID don't develop effective neutralising antibodies at all. To recover from a disease like this you have to develop an effective immune response, so if it's not antibodies, it has to be T-cell immunity. Moreover, even for antibody immunity it's not the whole story, because it's normal and expected for antibody count to decline with time — we have memory cells that ensure rapid production of the relevant antibody when the same antigene is presented.
It's basically the case of paying attention to something we can measure just because we can measure it.
A few things to remember. Antibodies dont stay expressed for high amounts for long levels of time forever after infection - imagine if your body was 100% against every infection you ever encountered forever? The important factor is that your body remembers what antibody to make and then makes it when the next infection happens. Depending on the sensitivity of the test you might not see a response. And a second important point - antibody mediated immunity is just one form of immunity. Cell mediated immunity definitely plays a role against coronavirus [1] and this doesnt test for the presence of reactive T cells etc. We arent getting a complete picture.
Also, if 5% of people have been infected, and all of them make antibodies, then that means herd immunity is still reachable. We dont have the data we need to figure out the complete fraction. And of course, a vaccine will help us artificially boost our way to herd immunity.
Antibody levels are often cited as prediction surrogates early on because they are easy to measure. Occurrence or recurrence of infection, irrespective of antibody levels, of course, takes time. Also remaining to be seen is the role of T-cell mediated immunity in reducing the severity of Covid infection. If that role is significant, then declining antibody levels may be less worrisome than people believe currently.
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