COVID, immunity and vaccines (no politics, science question)

Discussion in 'Hangar Talk' started by tspear, Jan 3, 2021.

  1. tspear

    tspear Pattern Altitude PoA Supporter

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    I have seen previous estimates that likely between 60 and 80% of the population needs to have "immunity" to break the epidemic. Most have stated there is not enough evidence to pin it down further yet.

    With about 95% effectiveness for the first two mRNA vaccines you need between roughly 63 and 84% of the population to break the pandemic.

    So two questions, First one; with the new strain out of Great Britain, which is some reports is almost twice as contagious. What does that do to the herd immunity numbers?
    Two, vaccines like the Astra Zenica which are only 62% effective, could they ever "break" the pandemic?

    Tim
     
  2. WannFly

    WannFly Final Approach

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    On kinda similar note, if I get vaccinated, can I still get covid ?
     
  3. Cap'n Jack

    Cap'n Jack Final Approach PoA Supporter

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    To the best of my knowledge, they are still evaluating how contagious the new strain might be, also also the effectiveness of the various vaccines against this new strain. Astra Zeneca isn't the only one coming, and the two vaccines being administered in the USA, Moderna and Pfizer, have higher efficacy rates than the numbers you stated for the AstraZeneca (AZ) product. There was a dosing for the AZ product that gave 90% efficacy (https://blogs.sciencemag.org/pipeli.../the-oxford-astrazeneca-vaccine-efficacy-data).

    Define "get COVID". Do you mean "get sick from it" or become a carrier for a short time if exposed?
    Edit: see reply below
     
    Last edited: Jan 3, 2021
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  4. Bob Noel

    Bob Noel Touchdown! Greaser!

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  5. 455 Bravo Uniform

    455 Bravo Uniform En-Route

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    I recovered last month. They say my antibody immunity lasts 3 months. Will the vaccine only be effective for 3 months?
     
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  6. Cap'n Jack

    Cap'n Jack Final Approach PoA Supporter

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  7. FormerHangie

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    Yes, the vaccine is not 100% effective, which is why it is advantageous to have as large percentage of the population vaccinated as possible. If you're in the 5% or so that didn't get immunity, it's helpful that those who did develop immunity won't be infectious.
     
    Last edited: Jan 3, 2021
  8. X3 Skier

    X3 Skier En-Route PoA Supporter

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    Since my last COVID thread was closed (COVID Vaccine (2)), this as good a place as any.

    I’m scheduled to be unblinded from the Moderna Trial Tuesday. I believe it will confirm I got the Vaccine back in Sept. On the slim chance I got the Placebo, I’ll get the first dose then.

    Be back Tuesday with the result.

    Cheers
     
  9. Llewtrah381

    Llewtrah381 Pre-Flight

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    Be careful: what they actually say is antibody TITERs (“detectable antibodies”) last three months. That’s entirely different than IMMUNITY. Our bodies make several antibodies in response to an initial infection (typically IgM then IgG), which both decline over time BUT the process is more complicated: what happens is the white blood cells which make the “effective” antibody (think of it as the cell that has the right key for that virus’ lock) changes to making ONLY that key and becomes what’s called a plasma cell. That creates a “memory” to produce those antibodies when you’re re-exposed to the same invader: those plasma cells stick around for variable times but typically years or even decades. The level of circulating antibodies naturally drops off but that doesn’t at all mean the plasma cells have stopped “standing guard”. That’s true for antibodies made from natural infection or via vaccine.

    This is a very simplistic description but basically I don’t personally worry at all about the findings that antibody TITERs go down after a few months - that’s common. If one has made antibodies the individual is very likely to have lasting immunity to THAT virus (technically, that protein) regardless of how the antibodies were triggered.
     
  10. woodchucker

    woodchucker Pattern Altitude

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    If someone knows different, please correct me, but it’s my understanding that you can still contract the virus after being vaccinated, but the vaccination mostly prevents you (if in the 95%) from becoming symptomatic. However, you can transmit the virus asymptotically to others. Basically the vaccine is to keep you out of the hospital and alive. But if that is true then mask wearing and social distancing won’t go away until herd immunity is reached ... which won’t be for a while. Realistically 2022 maybe? I’m hoping the government throws in some sort of small financial incentive to help convince people to take the vaccine.

    I should be getting my first dose by the end of the month.
     
  11. Palmpilot

    Palmpilot Touchdown! Greaser! PoA Supporter

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    I was under the impression that it's not yet known whether or to what extent the vaccines prevent you from transmitting the virus to others.
     
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  12. weilke

    weilke Touchdown! Greaser!

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    Yes.

    The approval trials did not test for this question. Now that millions of people are getting vaccinated, we should start to see data from outbreak investigations that tells us to what degree the vaccine is 'sterilizing'.
     
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  13. 455 Bravo Uniform

    455 Bravo Uniform En-Route

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    Thank you.
     
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  14. TommyG

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    The other question is, how long is the vaccine good for? Is it gonna be a yearly thing like the current flu vaccine, is it a lifetime protection?

    and even people that had COVID, even after the antibodies fade out, can they get it again? And if so does it come back stronger or less potent.

    Those two things will really affect herd immunity timeline.
     
  15. asicer

    asicer Final Approach

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    Isn't that assuming that the entire population exhibits the same behavior patterns? For example I would imagine that vaccinating frontline high-touch personnel would contribute more to that end than the newborn that never leaves mother's arms, the hermit whose only contact with the outside world is Instacart/Amazon/PoA or the guy that isn't expected to live into next month, no?
     
  16. tspear

    tspear Pattern Altitude PoA Supporter

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    The AZ vaccine as approved in Britain is only 62% effective. The 90% efficacy was on a smaller sample size of 3000 which is considered by all epidemiologist I have read as too small a sample size to determine anything except a follow-up study is needed.

    Tim

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  17. tspear

    tspear Pattern Altitude PoA Supporter

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    The point is to have enough of a large sample size to balance most of that out. Further traditional vaccine studies for the initial phase 3 trials are 18 to 65 (I think) plus most also require healthy candidates which eliminate many conditions such as diabetes.

    The result is we actually do not have data on the efficacy of any vaccine being now administered to the elderly, for all we know they could be as effective as a saline shot. Also there is a priority in many states and the proposed CDC guidelines for those with comorbidities (sp?). The result, we are really beta testing the vaccine on the general public.

    Tim

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  18. tspear

    tspear Pattern Altitude PoA Supporter

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    Also. Still no one has taken on the science question. If the vaccine is only 62% efficacy can it break the pandemic?
    And with anti-vaxer sentiment, even the more efficient mRNA can we break the pandemic?

    Tim

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  19. Matthew Rogers

    Matthew Rogers Line Up and Wait

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    They have. Moderna’s vaccine was shown to prevent symptoms in 94% of people, but prevent serious symptoms in 100% of people.

    If Astra’s vaccine is also 100% effective at preventing serious symptoms, then it will be easier to break the pandemic as nobody with the vaccine will be hospitalized. It then ACTUALLY becomes no worse than the flu as you only need to get the vaccine to be protected and then don’t have to worry about hospitals filling up and people dying. At that point, anti-vaxxers will not be as much of an issue as only they will be in the hospital and the general population does not need to be as worried about them spreading it around.

    So we just need to find out from more data if the “less” effective vaccines also prevent serious symptoms in 90+% or greater of cases. If so, then we may have a good path towards recovery.
     
  20. Bob Noel

    Bob Noel Touchdown! Greaser!

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    um, don't forget that people with influenza get hospitalized - according to the CDC, in the 2018-2019 flu season (which isn't 12 months long), there were almost 500,000 hospitalization because of influenza.
     
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  21. Matthew Rogers

    Matthew Rogers Line Up and Wait

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    And we also don’t have near 100% flu vaccination rates. And the flu vaccine is not nearly 95% effective each year.

    But even with that, doctors on this forum have stated that those who get the vaccine are never (not statistically, but they seem to see only bad flu cases from in-vaccinated people) those in the hospital and dying from the flu. So the relatively ineffective flu vaccine still has a great effect on keeping people from dying or being hospitalized.
     
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  22. midwestpa24

    midwestpa24 En-Route

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    I get what you are saying scientifically. However COVID appears to be breaking the norms. There have been numerous cases of people contracting COVID more than once, including two personal acquittances of mine that were sick and tested positive for COVID 3-4 months ago, recovered, then have become very ill and tested positive again. Immunity does not appear to be guaranteed for some reason.
     
  23. Patrick Rolle

    Patrick Rolle Filing Flight Plan

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    Interesting
     
  24. Patrick Rolle

    Patrick Rolle Filing Flight Plan

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    From my understanding, as long as the current vaccine is effective against the current/similar strain, immunity will last forever. As strains begin to change it may be necessary to have different types of vaccines, which are predicted yearly and geographically, much like what occurs with the flu.
     
  25. Ravioli

    Ravioli Final Approach PoA Supporter

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    The flu vaccine is actually different every year because the virus mutates. The efficacy of the flu vaccine varies from year to year based on how well the scientists guess (wait, no guessing in science) model the coming strain. If it were ever actually the exact same vaccine as any previous year they would do the ethical and non-profitable thing of saying, "No need for a vaccine this year if you took it in year yyyy."
     
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  26. tspear

    tspear Pattern Altitude PoA Supporter

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    I have yet to see anything which predicts how long immunity (if it occurs) which is anything but a guess based on previous vaccines. Problem is the mRNA vaccines which are the most effective have never been previously approved. So all we have are educated guesses; with most of the ones I have read/seen stating one to three years as the most likely period.

    Tim
     
  27. tspear

    tspear Pattern Altitude PoA Supporter

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    Science is full of guessing. e.g. one core tenant, such postulating a hypothesis is based on a guess (supposed to be an educated guess, but still a guess). Only the general public thinks we already know everything.

    Tim
     
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  28. GaryM

    GaryM Pre-takeoff checklist

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    There is good reason to be optimistic about how long the immunity will last, but a lot of that depends on the virus, and how fast it evolves the spike proteins that the vaccines are targeting. So far, the mutations seen don't seem to be able to elude immune response, whether from a vaccine or from a previous infection. But, as Tim notes, it'll be awhile before we have long-term data.

    The mRNA technology allowed for freakishly-fast development of the first vaccine candidates, but there is no mRNA in the vaccine; that's just how the antigens were developed. I don't think the immune system cares what underlying technology was used.
     
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  29. Tarheelpilot

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    I wonder if medical research in China has anything to do with how robust and persistent the virus is in the population.
     
  30. Llewtrah381

    Llewtrah381 Pre-Flight

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    I’ve tried to look at the literature about the recurrences (medical stuff - not the popular press). Best I can tell, of the tens of millions of cases worldwide there have been an almost literal handful of true recurrences. Most “recurrences” have ultimately been determined to be relapse (same infection was smoldering then flared up rather than having been completely cleared and a NEW exposure causes a new infection), from what I see.

    Of the true reinfections, the one article I saw from October, in The Lancet, identified four people worldwide with confirmed reinfection. Of those four there was no documented positive antibody after the first infection (two were documented as negative and two were “N/A”).

    That’s not yet conclusive, of course, but it sure suggests that having antibodies gives immunity. Remember, not everyone develops effective antibodies against a given infection: some people have conditions (including age) which suppress their immune response and sometimes the body just makes the wrong antibodies. And even having the right antibodies by testing doesn’t 100.000% prevent infection for pretty much any disease, because of compromised immune systems, etc.

    Think about that, though: whereas the vaccines are apparently giving around 95% immune response, natural infection in tens of millions of people has NOT given it in a literal handful.

    https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30783-0/fulltext

    Frankly, we should also be testing for antibodies, not just the virus. It’s cheap, quick, and can be done with a drop of blood. It would make WAY more sense to test people for antibodies instead of current infection before stepping into an airport, for example. Frankly, I’m not personally sure how I see we can get back to “normal” without extensive antibody testing, even if we could immunize the whole population. Remember: at 95%, one in twenty people won’t be protected.

    https://www.fda.gov/news-events/pre...rizes-first-point-care-antibody-test-covid-19
     
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  31. chemgeek

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    The canonical relationship for herd immunity for is 1-1/Ro, where Ro is the reproduction number of the infectious agent. Ro is difficult to accurately estimate, but is typically derived from the rate of spread of an infectious disease in the initial, exponential phases of growth, before the population has achieved significant immunity, and before mitigation efforts occur, which can reduce the effective reproduction number, R. The literature estimate of Ro for SARS-CoV-2 vary from 2.2-5.7, depending on locality. In the U.S., the initial exponential phases of epidemic growth in most states was between 2-3. So using value of 2-3, we arrive at a herd immunity level of 50-67%. If you figure in vaccine efficiency, E, then the value is [1-1/Ro]/E. So for vaccines with an average efficiency of 90% we would need to achieve vaccination rates of 55-75% to achieve herd immunity, which would essentially stamp out spread of the disease. If viral variants evolve to be slightly more contagious (larger Ro value), then of course the objectives for herd immunity increase commensurately. Depending on the numbers one assumes, it is possible that immunity rates as high as 95% may be required to stop more widespread outbreaks. One must also consider the non-uniformity of immunity. Some communities have had much higher natural exposure levels than others, and undoubtedly, some communities will have different compliance rates for vaccination. Communities with lower levels of immunity (natural or otherwise) will still be at risk for local outbreaks.
     
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  32. chemgeek

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    In both the Pfizer and Moderna Phase 3 trials, a significant fraction (around 5% or so) of participants in the experimental group contracted COVID. That is why the reported efficacy was less than 100%. There were few or no cases of severe disease in the experimental groups, which is a good result. Until we achieve high vaccination rates, and have good evidence that vaccines prevent infection as well as symptomatic disease, one should consider vaccines as primarily serving as personal protection rather than an immediate end to the pandemic.
     
  33. bflynn

    bflynn Final Approach

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    Question - if the science didn't test for this, how can you categorically state yes as the answer? It seems like the best answer based on limited testing is "uncertain, ask again".

    The concern in the world of vaccines is called "shedding" and the question is - can someone who has been vaccinated against covid carry and shed the virus. Vaccine research suggests this is very unlikely. The only time it's ever been observed to have happened involves live virus vaccines. None of these are live virus vaccines.

    BTW, AstraZenaca is reproving their vaccine under the half dose / full dose interval that was accidently discovered during their initial phase 3 trial. That method should be about 90% effective. The vaccine is already approved in Britian and is expected to be considered in the US next month. At this point it's a paperwork problem.

    For herd immunity, an additional wildcard factor is that it appears there many be some natural immunity to covid already. An early test used blood samples from 2016-2018 (pre covid) and the control group found that just under half the blood samples already had immunity. That may explain why the virus comes in waves as people develop immunity to it, but it never comes close to the expected herd immunity levels.
     
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  34. chemgeek

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    Long-term immunity is a little more complicated than neutralizing antibody titers. The initial immune response involves production of IgM antibodies, which do not last long, followed by IgG antibodies, which will persist at a useful level for maybe 3-6 months for coronaviruses as you have been informed. However, you will also produce memory cells that will "remember" how to make the neutralizing antibodies should the same infectious agent appear again. These memory cells will persist for a longer period of time than the IgG antibodies, and will be ready to spring into action when needed as long as they are present. How long these memory cells will meaningfully persist is not known for SARS-CoV-2, but based on the observation that there have been very few re-infected individuals for SARS-CoV-2 to date, it would appear that meaningful immunity may last at least 9-12 months. Other coronaviruses that cause the common cold do not produce immunity that lasts more than 6 months or so, so it is likely that it will be necessary to receive booster immunizations periodically in order to maintain longer term immunity to SARS-CoV-2. It seems unlikely that the virus will ever be eradicated, like smallpox or (almost) polio. We are going to be learning a lot more on the fly in the next few years. One of the goals of the Phase 3 trials that will go on for 2 full years is to track the immune responses of volunteers to be able to definitively assess the durability of immunity. This will be important data for devising proper schedules for booster immunizations.
     
    Last edited: Jan 5, 2021
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  35. chemgeek

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    There may also be an additional complication relating to differences in both levels and durability of immunity in naturally infected and vaccinated populations. For SARS-CoV-2 (and in general for other viral diseases) vaccination stimulates much higher levels of neutralizing antibodies and memory cells than natural infection. There is also some precedent from other viral diseases that asymptomatic or mild infections may not develop as robust immunity as more severe cases. I don't think there have been any published studies of this to date, however.

    Regarding serology studies, there is some potential cross-reactivity between neutralizing antibodies for the other 4 commonly occurring strains of coronaviruses that cause some common colds. Individuals with immunity to these harmless coronaviruses might "get lucky" on occasion and have antibodies and/or memory cells with some capacity to neutralize SARS-CoV-2 sufficient to prevent severe disease.
     
  36. chemgeek

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    Yes. With the currently approved mRNA vaccines, Phase 3 studies show that about 5% of participants contracted infections after completing their vaccination schedule, but the vast majority of those were mild cases. So the level of protection is quite good, nearly 100% from serious risk or mortality or long-term morbidity.
     
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  37. bflynn

    bflynn Final Approach

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    Hmmm, so in isolating everyone and not spreading the common cold around, we might have wiped out that as a neutralizing agent.

    I wonder if it works in reverse too? Will the covid vaccine work against the common cold, at least a little?
     
  38. WannFly

    WannFly Final Approach

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    Thanks everyone. i was referring to both serous complications from Covid as well as spreading the joy inadvertently. sounds like one can still be a carrier after the vaccination.
     
  39. Palmpilot

    Palmpilot Touchdown! Greaser! PoA Supporter

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    I've heard that some antibody tests are more accurate than others. Do you have any information on which ones provide the fewest false positives and false negatives?
     
  40. Llewtrah381

    Llewtrah381 Pre-Flight

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    I don’t. But the technology for this stuff in general has advanced a lot, so I’d actually be surprised if there weren’t good, inexpensive, easy-to-do tests with very high specificity (low false positives) and sensitivity (low false negatives). Think about it: affordable over-the-counter pregnancy tests have been available for a while with very good specificity and sensitivity. This is essentially the same technology - just looking for a different protein. I’d be surprised if the FDA approved a test that didn’t have very high performance, given the need for reliable results and the current technology.
     
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