5 ms·

Does anyone know if PCR tests will find out if you've had the virus, after you had the vaccine?

OldManAndTheCpp 5y ago
I got a rapid test after getting the first vaccine -- I was told that there were more than one type of antibodies, the vaccine only provides one, so they can test for the others to see if you had the virus proper.
ilogik 5y ago
PCR tests only detect live virus, not antibodies. there are several antibody tests for covid. As far as I'm aware, the vaccines only trigger the anti-spike protein antibodies, so if you test positive for other types of covid-19 antibodies, you've probably had it.
- rimliu 5y ago
  PCR test detect genetic material of the virus. It may be live virus it may be just fragments, impossible to tell.
olivierlacan 5y ago
PCR tests don't detect antibodies, they detect active virus. Antibody tests may be what you're thinking of. See: https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics https://www.fda.gov/consumers/consumer-updates/coronavirus-d... I don't know the answer to your question, but it would make sense unless the antibody test(s) look for a specific type of antibody to COVID-19 that is produced naturally when infected and not just any antibodies that might be produced when vaccinated.
- toolz 5y ago
  incorrect, PCR tests detect any virus matter - active or otherwise. This is a very important distinction since we've seem to lost our minds collectively and label PCR tests with a cycle threshold of >40 as a true positive.
  - mlyle 5y ago
    "lost our minds collectively" -- no, made a sane tradeoff in the sensitivity vs. specificity ratio when the disease is common. It's not like the sensitivity is wonderful even with a large number of PCR cycles, and the false positive rate was not too bad. As the disease becomes less common, it makes sense to turn down the sensitivity of the test. Base rate fallacy, yada yada.
    - toolz 5y ago
      here's a study showing above CT 32 not a single live virus was able to be cultured [1] - if this study accurately portrays reality then there's nothing resembling sanity with PCR CTs >40 https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1579/5937368 https://academic.oup.com/cid/advance-article/doi/10.1093/cid... (image from the study) https://i.imgur.com/AaZZIXM.png https://i.imgur.com/AaZZIXM.png
      - mlyle 5y ago
        People who are infected will not necessarily have a single live virus in a swab you collect. Yes, if you can't culture it, they probably are not infectious right now but that is a different distinction. You're also putting a whole lot of weight on a study with what, about 50 total positives? And of them, very few with a Ct of over 35.
        toolz 5y ago
        do you know of a study that shows the opposite? Because I know of more studies that have similar findings. here's one I found with a quick google (haven't read the study) https://pubs.acs.org/doi/10.1021/acsomega.1c00166 https://pubs.acs.org/doi/10.1021/acsomega.1c00166
        mlyle 5y ago
        Even your studies show a relatively low false positive rate with high numbers of cycles, and it's hoped that it increases sensitivity. No, we have no perfect data, because we have no perfect "infection test". High sensitivity was very worthwhile early in the pandemic, when infection was common and the predictive value of a test with a somewhat higher false positive rate was still high. Now that COVID is becoming rarer, we should absolutely be reducing cycle counts. The target should be to keep >75% of positives with actual infection even as the underlying rate of the disease decreases. I think we've exceeded this threshold by a large margin thus far. If you have a cogent statistical argument that disagrees instead of handwaving about cycle counts, I'm willing to listen.
checker659 5y ago
Find a lab that offers Roche Anti-Sars-cov2-N test.
- andy_ppp 5y ago
  Interesting, is this one just for Pfizer as I've had Astra Zenica which I believe is a different set of spike protein DNA sequences?
  - checker659 5y ago
    This one's for the nucleocapsid protein. If you'd like to test antibody generated by the vaccines, you'd have to take the Anti-sarscov2-S test.
  - fsh 5y ago
    All currently used vaccines use the same version of the spike protein sequence.
    - amluto 5y ago
      Incorrect. Pfizer, Moderna, and J&J use a pre-fusion stabilized sequence. AZ does not. However, all currently used vaccines are just the spike (S) protein plus possible non-COVID proteins (in the viral vector vaccines), so none will induce antibodies against the COVID N protein. I imagine it might be possible to guess whether someone was vaccinated with the AZ vaccine based on whether they have antibodies that are specific to the site that’s modified in the stabilized sequences. I don’t think anyone does a test like that.
Hard_Space 5y ago
My girlfriend got infected about ten days after my second AstraZeneca jab. We didn't isolate. I got tested: - Zero naturally-occurring antibodies (the kind you would get from having had COVID). - Strong presence of vaccine-induced antibodies. However, given the timing, I am still uncertain as to whether I contracted COVID during that post-second-jab 4 weeks when my girlfriend was infected (I gave blood for the test while I was still feeling bad in the weeks after the second injection, and I didn't spring for the 'currently infected' test, since the whole package of tests was pretty expensive). If I got COVID now, would it not be handled exclusively by vaccine-induced antibodies, which means that any test for having had COVID in the future would still be negative? I'm no kind of doubter, and I'm pretty sure the AZ double-jab helped me lately, but I'm not sure I'll ever know if I was ever infected, to be honest.
- hef19898 5y ago
  Even if you were, if you didn't have any symptoms the vaccine did it's job. In which case you were not infectious neither. I hope you better half fully recovered by now.
rootusrootus 5y ago
PCR, no, antibody tests do. E.g. if you give blood with the Red Cross right now, they will do a basic antibody test that will react if you have had COVID or if you have been vaccinated. If you test positive for that, they do a second test that will only react if you have been exposed to the real virus.

I got a rapid test after getting the first vaccine -- I was told that there were more than one type of antibodies, the vaccine only provides one, so they can test for the others to see if you had the virus proper.

ilogik 5y ago

PCR tests only detect live virus, not antibodies. there are several antibody tests for covid. As far as I'm aware, the vaccines only trigger the anti-spike protein antibodies, so if you test positive for other types of covid-19 antibodies, you've probably had it.

rimliu 5y ago
PCR test detect genetic material of the virus. It may be live virus it may be just fragments, impossible to tell.

olivierlacan 5y ago

PCR tests don't detect antibodies, they detect active virus. Antibody tests may be what you're thinking of. See: https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics https://www.fda.gov/consumers/consumer-updates/coronavirus-d... I don't know the answer to your question, but it would make sense unless the antibody test(s) look for a specific type of antibody to COVID-19 that is produced naturally when infected and not just any antibodies that might be produced when vaccinated.

toolz 5y ago
incorrect, PCR tests detect any virus matter - active or otherwise. This is a very important distinction since we've seem to lost our minds collectively and label PCR tests with a cycle threshold of >40 as a true positive.
- mlyle 5y ago
  "lost our minds collectively" -- no, made a sane tradeoff in the sensitivity vs. specificity ratio when the disease is common. It's not like the sensitivity is wonderful even with a large number of PCR cycles, and the false positive rate was not too bad. As the disease becomes less common, it makes sense to turn down the sensitivity of the test. Base rate fallacy, yada yada.
  - toolz 5y ago
    here's a study showing above CT 32 not a single live virus was able to be cultured [1] - if this study accurately portrays reality then there's nothing resembling sanity with PCR CTs >40 https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1579/5937368 https://academic.oup.com/cid/advance-article/doi/10.1093/cid... (image from the study) https://i.imgur.com/AaZZIXM.png https://i.imgur.com/AaZZIXM.png
    - mlyle 5y ago
      People who are infected will not necessarily have a single live virus in a swab you collect. Yes, if you can't culture it, they probably are not infectious right now but that is a different distinction. You're also putting a whole lot of weight on a study with what, about 50 total positives? And of them, very few with a Ct of over 35.
      - toolz 5y ago
        do you know of a study that shows the opposite? Because I know of more studies that have similar findings. here's one I found with a quick google (haven't read the study) https://pubs.acs.org/doi/10.1021/acsomega.1c00166 https://pubs.acs.org/doi/10.1021/acsomega.1c00166
        mlyle 5y ago
        Even your studies show a relatively low false positive rate with high numbers of cycles, and it's hoped that it increases sensitivity. No, we have no perfect data, because we have no perfect "infection test". High sensitivity was very worthwhile early in the pandemic, when infection was common and the predictive value of a test with a somewhat higher false positive rate was still high. Now that COVID is becoming rarer, we should absolutely be reducing cycle counts. The target should be to keep >75% of positives with actual infection even as the underlying rate of the disease decreases. I think we've exceeded this threshold by a large margin thus far. If you have a cogent statistical argument that disagrees instead of handwaving about cycle counts, I'm willing to listen.

checker659 5y ago

Find a lab that offers Roche Anti-Sars-cov2-N test.

andy_ppp 5y ago
Interesting, is this one just for Pfizer as I've had Astra Zenica which I believe is a different set of spike protein DNA sequences?
- checker659 5y ago
  This one's for the nucleocapsid protein. If you'd like to test antibody generated by the vaccines, you'd have to take the Anti-sarscov2-S test.
- fsh 5y ago
  All currently used vaccines use the same version of the spike protein sequence.
  - amluto 5y ago
    Incorrect. Pfizer, Moderna, and J&J use a pre-fusion stabilized sequence. AZ does not. However, all currently used vaccines are just the spike (S) protein plus possible non-COVID proteins (in the viral vector vaccines), so none will induce antibodies against the COVID N protein. I imagine it might be possible to guess whether someone was vaccinated with the AZ vaccine based on whether they have antibodies that are specific to the site that’s modified in the stabilized sequences. I don’t think anyone does a test like that.

Hard_Space 5y ago

My girlfriend got infected about ten days after my second AstraZeneca jab. We didn't isolate. I got tested: - Zero naturally-occurring antibodies (the kind you would get from having had COVID). - Strong presence of vaccine-induced antibodies. However, given the timing, I am still uncertain as to whether I contracted COVID during that post-second-jab 4 weeks when my girlfriend was infected (I gave blood for the test while I was still feeling bad in the weeks after the second injection, and I didn't spring for the 'currently infected' test, since the whole package of tests was pretty expensive). If I got COVID now, would it not be handled exclusively by vaccine-induced antibodies, which means that any test for having had COVID in the future would still be negative? I'm no kind of doubter, and I'm pretty sure the AZ double-jab helped me lately, but I'm not sure I'll ever know if I was ever infected, to be honest.

hef19898 5y ago
Even if you were, if you didn't have any symptoms the vaccine did it's job. In which case you were not infectious neither. I hope you better half fully recovered by now.

rootusrootus 5y ago

PCR, no, antibody tests do. E.g. if you give blood with the Red Cross right now, they will do a basic antibody test that will react if you have had COVID or if you have been vaccinated. If you test positive for that, they do a second test that will only react if you have been exposed to the real virus.