Dropping Antibody Levels

[iluv2travel]

... so it does seem, as you suggest, that the man had no measurable antibodies on 5/26 (when he had the second negative test), was reinfected soon after,

It seems that he probably was only able to be reinfected because he didn't produce antibodies the first time around.

I don't think there's ever been a case where a person was antibodies positive and COVID negative at least a few days prior to a reinfection.

[biobook]

It seems that he probably was only able to be reinfected because he didn't produce antibodies the first time around.

Well, we don't have any evidence to conclude that.  The effectiveness of any chemical in the body, or any drug we introduce into the body, is going to depend on the dose, or the amount.  A baby aspirin might not cure your headache, but a larger dose will.  It's possible that he did produce antibodies first time around, but a few weeks later they had declined to too low of a dose to effectively fight off infection.

I don't think there's ever been a case where a person was antibodies positive and COVID negative at least a few days prior to a reinfection.

There have been only 33 documented reinfections, and each one had different data collected about it, so it seems too early to say that there hasn't ever been such a case. 

I'll take a look at some of those 33 and see if any pop up.

[iluv2travel]

Well, we don't have any evidence to conclude that.  The effectiveness of any chemical in the body, or any drug we introduce into the body, is going to depend on the dose, or the amount.  A baby aspirin might not cure your headache, but a larger dose will.  It's possible that he did produce antibodies first time around, but a few weeks later they had declined to too low of a dose to effectively fight off infection.

Yes, that's a likely scenario as well.

There have been only 33 documented reinfections, and each one had different data collected about it, so it seems too early to say that there hasn't ever been such a case. I'll take a look at some of those 33 and see if any pop up.

Would be very interesting if there was a confirmed COVID negative plus confirmed antibodies positive followed by a new COVID positive while there is/was potentially still antibodies. This would obviously be something extremely rare at this point given that 33 confirmed reinfections as a whole is minuscule.

[gozalim]

It seems fair to say that we have not yet seen a single case worldwide where someone was antibody positive and was reinfected during that time.

(on the other hand there do seem to be some -very few- cases of general reinfection. both where no antibodies were ever recorded, as well as were antibodies had been previously been recorded but then dropped below detectable levels)

[biobook]

It seems fair to say that we have not yet seen a single case worldwide where someone was antibody positive and was reinfected during that time.

(on the other hand there do seem to be some -very few- cases of general reinfection. both where no antibodies were ever recorded, as well as were antibodies had been previously been recorded but then dropped below detectable levels)

There do seem to be a few cases that at least hint that someone was reinfected while antibody positive:

https://www.timesofisrael.com/81-israelis-suspected-of-being-reinfected-with-coronavirus-health-ministry/
Published in October:

They told the story of a 20-year-old woman from Bnei Brak, healthy until she caught the coronavirus. She was diagnosed on April 17, and tested negative on May 1 and May 10.

The doctors wrote: “During the first week of August 2020, after enjoying three months of health, some of her family members were symptomatic for COVID-19 and tested positive.” The patient then went for screening on August 6 and on August 11, and tested positive both times.

Asked how sure she is about the reinfection diagnosis, Nachmias told The Times of Israel: “There is no room for doubt, there was clearly reinfection. We did the first tests while she was diagnosed to have the disease clinically, then she was clearly negative, and she was subsequently infected.”

She said that upon the second infection, she had a blood sample drawn for analysis and found that antibodies were present. As most patients wouldn’t yet have antibodies so soon after infection, Nachmias said they were seemingly from the first infection, constituting extra evidence that the patient had, indeed, been infected back in April.

Another in Israel:
https://www.ynetnews.com/health_science/article/SJvLIxRnw

After being declared free of the virus the first time, the man was released back to the geriatric care facility where he lived, while two further coronavirus tests also returned a negative result.
But when a new outbreak of COVID-19 was detected in the facility, the man was tested once again and a positive result was returned....genetic testing at Sheba revealed that the second infection was from a different strain.
According to medical officials, the lab's findings were bolstered by the fact that the man had produced a small amount of antibodies after his first infection.

From England: A large study of health care workers.  1246 tested antibody-positive in April.  They were invited for PCR tests for virus every two weeks, and antibody testing every two months, but it's not clear to me whether they were actually tested that often.  3 of them had a subsequent positive PCR picked up by this repeated screening, suggesting reinfection, but they were all asymptomatic.
https://directorsblog.nih.gov/2020/12/08/study-of-healthcare-workers-shows-covid-19-immunity-lasts-many-months/
The researchers say that because of the small number of reinfections, they can't draw any conclusions about the relative importance of current or past antibody level or T cells in preventing reinfection. 
https://www.medrxiv.org/content/10.1101/2020.11.18.20234369v1.full

So at this point, reinfections are rare, but we can't point to a certain level of antibodies that prevents them from occuring.

[Dan]

No idea what my levels are, but just tested positive for antibodies some 11 months after I was infected.

[Euclid]

No idea what my levels are, but just tested positive for antibodies some 11 months after I was infected.

Did you need to transfer a credit line?

[etech0]

Did you need to transfer a credit line?

If you don't like your results, HUCA

[NTorch]

No idea what my levels are, but just tested positive for antibodies some 11 months after I was infected.

Great new study showing antibodies and immunity eight months post infection
https://science.sciencemag.org/content/early/2021/01/06/science.abf4063

Summarized in local newspaper
https://nypost.com/2021/01/07/covid-19-patients-still-immune-eight-months-after-infection-study/

[Ergel]

What does the below mean? That antibodies were present, but not enough to cross the threshold?

[Dan]

What does the below mean? That antibodies were present, but not enough to cross the threshold?

Yup

[Ergel]

Yup

She tested positive 2.5 weeks ago, I guess still developing?

[Dan]

Very likely

[biobook]

Very likely

Especially if it was a mild case.

"Most persons infected with SARS-CoV-2 display an antibody response between day 10 and day 21 after infection. Detection in mild cases can take longer time (four weeks or more) and in a small number of cases antibodies (i.e., IgM, IgG) are not detected at all (at least during the studies’ time scale)."
https://www.ecdc.europa.eu/en/covid-19/latest-evidence/immune-responses

[etech0]

I had a mild case, 1.5 months later had 7/15 aka negative for antibodies, 3.5 months after infection got a positive antibody result (different test, no number given).