It takes time for the body’s immune system to generate antibodies against a specific pathogen, antibody tests may be negative early in the course of infection; also antibody tests sometimes have trouble distinguishing between infections from closely related pathogens.
Great question. A quick answer seems to be no. It seems we need a way to detect the low-level, paracrine interferon communication that occurs between cells that are indicating a cell is fighting a viral infection. That said, we'll probably also need serological tests to identify and artificially reproduce the antibody as a treatment method.
Another potential approach is a lung (or lobe) delivery system. Let's discuss this more. - Rob
That's right. Those are the main limitations. Antibodies appear more than a week after the infection, so that's not optimal as a first line point of care diagnostic. Specificity problems exist, because you have to by definition pick up polyclonal reactivity from the serum. Your antigen needs to be long enough to bait enough of that to get a signal from most patients, but short enough to make it reasonably specific to the COVID19 virus. That's a balancing act that likely has no optimal solution. The makers of these kits do not seem to discuss any of these problems, which is probably a bad sign.
The upside is that you can tell a few things that PCR can't. You can tell whether you had the infection a long time after it cleared. This can help future epidemiologists make sense of what happened today. It can help the patient know that they are (more likely than not) protected from repeated infection. They can even tell you whether a vaccine is working as intended, in the absence of any virus.
But these advantages apply only if the test in fact achieves the necessary specificity. And that looks to me like a big question mark at the moment.
Thanks John (@John Schloendorn), very insightful. So do individuals typically produce the same antibodies to one particular virus or are the antibodies substantially different from individual to individual? If there are differences, do we know (or have evidence) for what causes these differences?
I agree that we need to get some data from the test makers (particularly specifics on the basis of the tests and as you point out how they rule out other similar coronaviruses etc.). Also, we need to be collecting data on the number of false positives and negatives we're having as a result of these tests. Has anyone seen the COVID-19 genome? What are the difference between this genome and other coronaviruses?
Thanks, hope we can continue this discussion. Best wishes, Rob
@ Petru Emil Muntean
The antibody produced to a particular virus is specific for that virus only and sometime even strain specific (this is why a new Influenza vaccine is produced every-year to include all the strains of viruses reported in previous year)
A validated SARS-CoV-2 specific antibody test (used for COVID-19) can:
1. Detect the exposure of a person to SARS-Cov-2, starting from 2nd week to anytime weeks later and can give the true prevalence of COVID-19 in the population.
2. Can give an idea of immunity to SARS-CoV-2 (although the duration of immunity for this infection is still unknown).
3. Can be helpful to check the success of any vaccine for COVID-19 (if and once a successful vaccine is available).
4. Can be able to identify people who have recovered from COVID-19. Many countries are (USA, UK, Germany) are even planning to issue an immunity passport based on this test, although WHO has been skeptical of this idea.
Less is known about whether presence of antibody response indicates protection from reinfection by SARS-COV-2, whether antibody response depends on the severity of illness, and the variation in the sensitivity test kits available for COVID-2.
Immune response is also expected to be poor in people on immunosuppressive drugs, immunodeficiency states, and elderly.
They detect antibody responses to the virus thus they are indirect evidence of the infection
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