The half-life of antibody levels has been estimated at 73 days. The antibody tests are quite sensitive, time has not been enough of a factor yet to produce false negatives. In a year or two it might be.
The only time concern is that you need to wait 2-3 weeks until after you recover from COVID to ensure you test positive.
It’s not clear yet how reliable the antibody tests are. Antibodies fade over time, and we don’t know how long Covid-19 antibodies remain detectable in your blood. It’s quite possible that after 6 weeks or so, you’ll no longer have easily detectable levels of antibodies.
How long after the illness did you have the antibody test taken? My wife was tested positive in April, had all the symptoms, so it is almost 100% sure that she actually had COVID-19. THe antibody test two weeks after the symptoms were gone was negative. The second antibody test a few days later was ambigous. She is planning to take a third antibody test next week.
How long after infection will an antibody test work? I have had 2 instances of suspected Covid infection, one where my friend who I had met outside for a walk actually tested positive. The latest was probably November 2020. Would I still be able to identify infection with the antibody test?
The whole antibody testing looks totally unreliable to me. My wife was tested COVID-19 positive about 4 weeks ago. So was her boss at a different test location, so I assume the test was correct. Also she was ill with the typical symptoms. Meanwhile she has recovered and three days ago she had and antibody test and the result was negative, not even close to the threshold.
> asymptomatic people may test positive for 1-2 weeks, while those with mild-to moderate disease often continue to test positive for a week or more after this.
Keep in mind individuals can test positive for months after being infected but are not at risk for spreading the virus. It really should be a negative test or 14+ days after a positive test.
A test months later would be negative (if it was a swab) they are only accurate in the first week or so.
The antibody tests are fraught with issues, and if you fight the virus with your T cells rather than B cells, the antibody test won't pick that up and you'll show as negative.
> It was reported that after SARS infection, IgM antibody could be detected in patient blood after 3-6 days and IgG could be detected after 8 days. Since COVID-19 belongs to the same large family of viruses as those that cause the MERS and SARS outbreak, we assume its antibody generation process is similar, and detection of the IgG and IgM antibody against SARS-CoV-2 will be an indication of infection.
Also keep in mind that the false negatives for the tests is pretty high, because the tests require a significant viral load in the blood and in some cases it can take several days after the symptoms set in.
The one time I had covid about a year ago the tests all showed positive withing about 30 seconds, and continued to do so for about 9 days even though I never had more than some congestion and a light cough. YMMV I guess?
> It takes a long time for the body to produce the antibodies after infection. This test is only 90% sensitive after 12 weeks
That's not much of a problem except for people worried about infection after a single known exposure (e.g. needlestick in a medical setting).
About a third of patients spontaneously clear the acute infection within six months. On top of that, some countries (such as Germany) refuse to treat acute infections with antivirals - so patients have to wait 6 months for the infection to develop into a chronic infection before they can take the medicine which cures it.
Yeah, there's a limited window over which antibody testing is useful. I hadn't heard that it was only a few months, but that wouldn't be shocking, especially if you want a low rate of false negatives. Hopefully someone reading this knows more than me about approaches to testing that might work over longer time scales and not be confused by vaccination.
The sample size is very small and they list other limitations to their findings, but:
"In conclusion, despite concerns of waning immunity, appropriate immunoassays can detect antibodies against SARS-CoV-2 at 8 months after infection in most asymptomatic or mildly symptomatic persons."
The half-life of antibody levels has been estimated at 73 days. The antibody tests are quite sensitive, time has not been enough of a factor yet to produce false negatives. In a year or two it might be.
The only time concern is that you need to wait 2-3 weeks until after you recover from COVID to ensure you test positive.
reply