Covid-19 test status after vaccination

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For someone who has been vaccinated against Covid-19, will a subsequent Covid test show up as positve? If so, how is it possible to have a negative test after being vaccinated?
 

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  • #2
phinds
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Don't' know the answer but not sure why it matters. If you've been vaccinated, the latest statistics are that your chances of getting Covid are 2 in 100,000 so why would you NEED a negative test?
 
  • #3
atyy
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For all vaccines, vaccination will not cause someone to test positive for COVID-19 on PCR tests, nor on antigen tests or antigen rapid tests.

Vaccination will cause someone to test positive on some antibody tests. However, the details depend on the vaccine and the test. The vaccine will give you antibody against parts of the virus, just as infection will. However, not all vaccines contain all components of the virus. So for example, with the Pfizer vaccine, you will test positive for antibodies against parts of the spike protein, but you will not test positive for antibodies against nucleocapsid proteins.
https://www.sciencedirect.com/science/article/pii/S1198743X21002895
https://www.news-medical.net/news/2...iffers-from-natural-SARS-CoV-2-infection.aspx
 
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  • #4
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For all vaccines, vaccination will not cause someone to test positive for COVID-19 on PCR tests, nor on antigen tests or antigen rapid tests.
Surely the antigen tests detect the presence of antibodies, which the vaccines stimulate the immune system to produce? I can see that the PCR test will do a better analysis though.
 
  • #5
atyy
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Surely the antigen tests detect the presence of antibodies, which the vaccines stimulate the immune system to produce? I can see that the PCR test will do a better analysis though.
No, the antigen tests are different from the antibody tests. The antigen tests detect whether a protein that is a part of the virus is present.

So both the antigen and PCR tests detect the presence of parts of the virus. The antigen detects proteins that are part of the virus, while the PCR test detects nucleic acids sequences that are part of the virus.
 
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Atyy: Thanks for your explanation...
 
  • #9
phinds
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Odd that 2 vaccinated people got the virus again. Makes me wonder if the 2 out of 100,000 statistic I read is really true.
 
  • #10
atyy
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Odd that 2 vaccinated people got the virus again. Makes me wonder if the 2 out of 100,000 statistic I read is really true.
Could they have been false positives?

False positive on a cruise: https://www.todayonline.com/singapo...dustry-means-test-protocols-and-improve-their

False positives in Nevada nursing homes: https://www.usatoday.com/story/news...ada-must-drop-antigen-testing-ban/5940391002/

The Pfizer vaccine gives about 86% protection against infection (asymptomatic, mild, severe) for earlier versions of the virus, but for the delta (B.1.617.2) and beta (B.1.351) variants, that falls to about 80% and 75% respectively.

delta variant: https://www.theguardian.com/world/2021/jun/15/the-covid-delta-variant-how-effective-are-the-vaccines

beta variant: https://www.nejm.org/doi/full/10.1056/NEJMc2104974
 
  • #12
russ_watters
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Odd that 2 vaccinated people got the virus again. Makes me wonder if the 2 out of 100,000 statistic I read is really true.
Since 95% (the stated efficacy of the Pfizer/Moderna vaccines) is 2 in 38, I wonder what the 2 in 100,000 stat means/comes from too.

I would guess that with 95% efficacy you would expect a cruise with 2 infected people embarking to debark dozens of infected people. I'm sure it is possible to re-model super-spreader events such as the Diamond Princess along such lines. I'd be very curios to see such a model...

A cruise ship would be complicated due to the duration and uncertainty of interaction, so there would be some complexity to the model. How about a choir practice? That was a single/discrete event with a single index case and 52 confirmed and assumed secondary cases. If everyone else in the group had been vaccinated, one would have expected the number to be 3 secondary cases (caveat: not sure if that includes spouse-to-spouse transmissions.
 
  • #13
phinds
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Since 95% (the stated efficacy of the Pfizer/Moderna vaccines) is 2 in 38, I wonder what the 2 in 100,000 stat means/comes from too.
I think maybe it was the number of DEATHS of vaccinated people who still contracted covid, but even that seems unrealistically low. Wish I could remember where I read it. I think it was a reputable publication but that doesn't mean the reporter didn't misreport something.
 
  • #14
russ_watters
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See late edit with a rough attempt at modeling...
 
  • #15
OmCheeto
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I think maybe it was the number of DEATHS of vaccinated people who still contracted covid, but even that seems unrealistically low. Wish I could remember where I read it. I think it was a reputable publication but that doesn't mean the reporter didn't misreport something.
According to the CDC, the ratio is about 1 death in 200,000 for fully vaccinated people.

As of June 14, 2021, more than 144 million people in the United States had been fully vaccinated against COVID-19.
...
Deaths† 671

ref: https://www.cdc.gov/vaccines/covid-19/health-departments/breakthrough-cases.html

144,000,000 / 671 = 214,000
 
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  • #16
OmCheeto
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According to the CDC, the ratio is about 1 death in 200,000 for fully vaccinated people.
Contracting covid once fully vaccinated is about 1 in 2000.

As of April 30, 2021, approximately 101 million persons in the United States had been fully vaccinated against COVID-19.

A total of 10,262 SARS-CoV-2 vaccine breakthrough infections had been reported from 46 U.S. states and territories as of April 30, 2021.

reference: https://www.cdc.gov/mmwr/volumes/70/wr/mm7021e3.htm?s_cid=mm7021e3_w
 
  • #17
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Is really 549 because you need to subtract the 122 cases where the patients died from something else.

In 3 months (my estimate of the time to look at vaccine statistics), there are about 850,000 deaths from all causes. There were about 60,000 deaths from Covid (highly dependent on where exactly the three month window is) and I am going to take the average vaccination rate as 40%. That lets one infer some approximate numbers. All numbers US.

Vaccinations have saved about 40,000 lives to date.

Vaccination reduces your odds of dying by about a factor of 75. (40000/549) This seems within the range of expectations.

If vaccinated, your odds of dying of Covid within the next year are 1:60,000. (Perhaps this is where 2 per 100,000 comes from) - 549 deaths per three months x one year / 330 million x 40%. I don't think this is a very useful number - if you're 21 and healthy, your odds are already less than that. The number integrates over way too many things.
 
  • #18
atyy
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https://www.cdc.gov/mmwr/volumes/70/wr/mm7021e3.htm
"The findings in this report are subject to at least two limitations. First, the number of reported COVID-19 vaccine breakthrough cases is likely a substantial undercount of all SARS-CoV-2 infections among fully vaccinated persons. The national surveillance system relies on passive and voluntary reporting, and data might not be complete or representative. Many persons with vaccine breakthrough infections, especially those who are asymptomatic or who experience mild illness, might not seek testing."
 
  • #20
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The findings in this report are subject to at least two limitations.
Sure, and these have been around since the beginning (although some were pooh-poohed then). Could my 40,000 be 30,000 or 50,000? Sure. 20,000 or 80,000? Maybe. 4000 or 400,000? Probably not.

Estimates flu and pneumonia deaths as 15 per 100,000 persons per year
That seems high. Converted to US numbers, 15 per 100K per year is 50,000 flu deaths. That's a bad flu season. Granted, you've tossed in pneumonia, but pneumonia is very often a complication of something else. So where it appears isn't always so well-defined.
36 deaths per 100,000 persons per year

That seems really, really high. Converted to US numbers, 36 per 100K per year is 120,000 Covid deaths/year. But, you say , Israel is not the US. Perhaps they have more Covid. It goes the other way: Israel has had 6500 deaths in 9 million people, and the US has had 95x as many deaths with 35x the population, so actually the extrapolation is 325,000 Covid deaths among a fully vaccinated US population per year. This says the vaccination buys a factor of 2.

I think I trust my 75x more than 2x.

Also, 325,00/year is 900/day. The US has been below this number since mid-March.
 
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  • #21
atyy
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That seems really, really high. Converted to US numbers, 36 per 100K per year is 120,000 Covid deaths/year. But, you say , Israel is not the US. Perhaps they have more Covid. It goes the other way: Israel has had 6500 deaths in 9 million people, and the US has had 95x as many deaths with 35x the population, so actually the extrapolation is 325,000 Covid deaths among a fully vaccinated US population per year. This says the vaccination buys a factor of 2.

I think I trust my 75x more than 2x.
Yes, it seemed high to me. But anyway, if we take the numbers in the study, they say vaccination reduces death rates by 96.7%, which is about 30x, closer to your 75x (although the other way of calculating gives 2x).
 
  • #22
Astronuc
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https://news.yahoo.com/coronavirus-infects-vaccinated-leader-florida-104727118.html
MIAMI (AP) — A vaccinated Miami-Dade county commissioner who helped other local officials in Surfside following the collapse of a condominium building announced that he and his chief of staff tested positive for COVID-19.

The news release late Sunday from Miami-Dade County Commission Chairman Jose “Pepe” Diaz said he and his chief of staff Isidoro Lopez, who also received a vaccine against COVID-19, came down with flu-like symptoms earlier in the day and later tested positive for the virus.

“Staff and others who have been in close contact with them will be getting tested between today and tomorrow,” the news release said. The statement also said Diaz and Lopez would be isolating and following guidelines from the Centers for Disease Control and Prevention.

So, some folks who have been vaccinated against SARS-COV-2 may also contract the virus and develop symptoms of COVID-19. Nevertheless, it appear to be relatively rare. I wonder if it is the Delta variant, and if that will be reported.

“Breakthrough” infections — fully vaccinated individuals who contract the coronavirus — do happen, although they are very rare. An Associated Press analysis of government data in May showed only about 1% of such cases resulted in hospitalization or death. The analysis suggested that nearly all COVID-19 deaths in the U.S. recently have been in people who weren’t vaccinated, a staggering demonstration of how effective the shots have been and an indication that deaths could approach zero if every eligible person gets the vaccine.

Last week, Florida health officials reported an increase in COVID-19 cases and a higher positive test rate compared with other recent weeks.
 
  • #23
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So, some folks who have been vaccinated against SARS-COV-2 may also contract the virus and develop symptoms of COVID-19.
I think that's what 95% effective means. :wink:
Nevertheless, it appear to be relatively rare.
I think that's what 95% effective means. :wink:

There is some idea in people's head that vaccines provide perfect protection, not substantially enhanecd protection.
 
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