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I know that seems like a large number but in the vaccine arm there were 20x more subjects and only 15 cases. So with the 1359 previously infected subjects, assu

by spion 5y ago

I know that seems like a large number but in the vaccine arm there were 20x more subjects and only 15 cases. So with the 1359 previously infected subjects, assuming identical behavior to vaccinated subjects, we would expect around 0.9 cases if vaccines were approximately equal to infection. So this study doesn't have enough statistical power to say how vaccines compare to previous infection. Could be better, could be up to 3 times worse within a high confidence interval. (disclamer: back-of-the-napkin math, did not double check everything)

phkahler 5y ago
>> So this study doesn't have enough statistical power to say how vaccines compare to previous infection. Could be better, could be up to 3 times worse within a high confidence interval. Could be. But it would be great if they'd just say having had a confirmed case is equivalent to getting the vaccine because several studies have now shown that to be roughly the case. It's also conventional medical wisdom although it varies by virus.
- cbsmith 5y ago
  Unfortunately, we have reason to believe that over time, the immune defenses from COVID-19 infection seem to decline, particularly in older folks. It'd be great if we had some definitive data on secondary infection rates, but until a lot more people get infected, we just won't have it.
  - barney54 5y ago
    What is the evidence that “we have reason to believe that over time, immune defenses from COVID-19 infection seems to decline”?
    - astrange 5y ago
      I think this is another case where improved surveillance is turning up things that, while they look bad, happen with other vaccines and never turn out to be a problem. The same goes for variants, which a lot of people expect to break through vaccines because that's how the flu works, but it doesn't actually seem like they will.
      - jkhdigital 5y ago
        Yes, the extreme focus of attention is turning routine and expected medical observations into scary anecdotal news cycles.
  - huffmsa 5y ago
    I keep hearing this, but have yet to see evidence that the elderly are catching second rounds at a high rate.
    - garmaine 5y ago
      Because there isn’t any. But that is how the aging immune system responds to most other diseases, so we assume the same will be true here.
- whoknowswhat11 5y ago
  No kidding. It's clear to me that protection at some level is provided following infection - which simply makes sense. You'll notice they say - we don't have enough data. Then data is incomplete. Then we can't really say because study was X / Y / Z. They ignore the MASSIVE difference in your chance of being infected if you are unvaccinated and have not been infected vs many other combos. Just treat folks who've been infected as vaccinated, they can get booster / variant shots with everyone else when the time comes.
  - johnchristopher 5y ago
    I'd like to know the death rate of infected unvaccinated people who get covid again against vaccinated people who get covid and get sick.
    - sgt101 5y ago
      According to this study it could be a long time before we know that - I think cov-19 in the presence of a non overwhelmed medical system armed with steroids and oxygen kills less than 2/100 infected folk so getting enough incidents in either of those arms of a trial is going to be hard work.
      - iso1210 5y ago
        The death rate for certain demographics (especially say over 70s) is far higher than 2-in-100. While some countries have high levels of vaccination - especially in those demographics - most don't. The UK is enterring a third wave, and has a high number of elderly people having been fully (2 shot, mainly AZ) vaccinated. Early indications are that those enterring hospitals now on the whole have not been fully vaccinated.
        benjaminwootton 5y ago
        And for most people under 70, it's way under that, FWIW.
- occamrazor 5y ago
  The rough consensus is that an infection is equivalent to a single dose of vaccine. Some countries do not give the second dose to previously infected people.
mnw21cam 5y ago
Here are the numbers: Total participants: 52238. Previously infected: 2579, of whom 1220 vaccinated, 1359 not vaccinated. No subsequent infections in either of these groups. Not previously infected: 49659, of whom 29461 vaccinated (15 subsequent infections), 20198 not vaccinated (2139 subsequent infections). Comparing previous infection with vaccination, we have 0/1359 infections in the previously infected and 15/29461 infections otherwise. According to Fisher's exact test, the two-tailed P-value for this is 1.0, which is very much not significant. You're correct to say that the study doesn't show how vaccines compare to previous infection. The study is way underpowered to show that. For the unvaccinated, it gets more interesting. We have 0/1359 infections versus 2139/20198. According to Fisher, that has a P-value of 2 * 10^-64, which is most definitely significant. The study is not underpowered to show this at all. A previous infection is definitely protective. With the caveat that the participants didn't have asymptomatic screening, so there is quite possibly bias due to people with a previous infection getting a second milder case and not being tested. Using the exact method, 95% confidence intervals for infection rate are: Previously infected, not vaccinated: 0% to 0.3% Previously infected, vaccinated: 0% to 0.3% Not previously infected, not vaccinated: 10.1% to 11.0% Not previously infected, vaccinated: 0.03% to 0.08%
- spion 5y ago
  Thanks for this! Yes there is no doubt that there is an effect, of course, but it doesn't rule out the booster shot being possibly very helpful in strenghtening immunity

by spion 5y ago

phkahler 5y ago

>> So this study doesn't have enough statistical power to say how vaccines compare to previous infection. Could be better, could be up to 3 times worse within a high confidence interval. Could be. But it would be great if they'd just say having had a confirmed case is equivalent to getting the vaccine because several studies have now shown that to be roughly the case. It's also conventional medical wisdom although it varies by virus.

cbsmith 5y ago
Unfortunately, we have reason to believe that over time, the immune defenses from COVID-19 infection seem to decline, particularly in older folks. It'd be great if we had some definitive data on secondary infection rates, but until a lot more people get infected, we just won't have it.
- barney54 5y ago
  What is the evidence that “we have reason to believe that over time, immune defenses from COVID-19 infection seems to decline”?
  - astrange 5y ago
    I think this is another case where improved surveillance is turning up things that, while they look bad, happen with other vaccines and never turn out to be a problem. The same goes for variants, which a lot of people expect to break through vaccines because that's how the flu works, but it doesn't actually seem like they will.
    - jkhdigital 5y ago
      Yes, the extreme focus of attention is turning routine and expected medical observations into scary anecdotal news cycles.
- huffmsa 5y ago
  I keep hearing this, but have yet to see evidence that the elderly are catching second rounds at a high rate.
  - garmaine 5y ago
    Because there isn’t any. But that is how the aging immune system responds to most other diseases, so we assume the same will be true here.
whoknowswhat11 5y ago
No kidding. It's clear to me that protection at some level is provided following infection - which simply makes sense. You'll notice they say - we don't have enough data. Then data is incomplete. Then we can't really say because study was X / Y / Z. They ignore the MASSIVE difference in your chance of being infected if you are unvaccinated and have not been infected vs many other combos. Just treat folks who've been infected as vaccinated, they can get booster / variant shots with everyone else when the time comes.
- johnchristopher 5y ago
  I'd like to know the death rate of infected unvaccinated people who get covid again against vaccinated people who get covid and get sick.
  - sgt101 5y ago
    According to this study it could be a long time before we know that - I think cov-19 in the presence of a non overwhelmed medical system armed with steroids and oxygen kills less than 2/100 infected folk so getting enough incidents in either of those arms of a trial is going to be hard work.
    - iso1210 5y ago
      The death rate for certain demographics (especially say over 70s) is far higher than 2-in-100. While some countries have high levels of vaccination - especially in those demographics - most don't. The UK is enterring a third wave, and has a high number of elderly people having been fully (2 shot, mainly AZ) vaccinated. Early indications are that those enterring hospitals now on the whole have not been fully vaccinated.
      - benjaminwootton 5y ago
        And for most people under 70, it's way under that, FWIW.
occamrazor 5y ago
The rough consensus is that an infection is equivalent to a single dose of vaccine. Some countries do not give the second dose to previously infected people.

mnw21cam 5y ago

Here are the numbers: Total participants: 52238. Previously infected: 2579, of whom 1220 vaccinated, 1359 not vaccinated. No subsequent infections in either of these groups. Not previously infected: 49659, of whom 29461 vaccinated (15 subsequent infections), 20198 not vaccinated (2139 subsequent infections). Comparing previous infection with vaccination, we have 0/1359 infections in the previously infected and 15/29461 infections otherwise. According to Fisher's exact test, the two-tailed P-value for this is 1.0, which is very much not significant. You're correct to say that the study doesn't show how vaccines compare to previous infection. The study is way underpowered to show that. For the unvaccinated, it gets more interesting. We have 0/1359 infections versus 2139/20198. According to Fisher, that has a P-value of 2 * 10^-64, which is most definitely significant. The study is not underpowered to show this at all. A previous infection is definitely protective. With the caveat that the participants didn't have asymptomatic screening, so there is quite possibly bias due to people with a previous infection getting a second milder case and not being tested. Using the exact method, 95% confidence intervals for infection rate are: Previously infected, not vaccinated: 0% to 0.3% Previously infected, vaccinated: 0% to 0.3% Not previously infected, not vaccinated: 10.1% to 11.0% Not previously infected, vaccinated: 0.03% to 0.08%

spion 5y ago
Thanks for this! Yes there is no doubt that there is an effect, of course, but it doesn't rule out the booster shot being possibly very helpful in strenghtening immunity