2019 Novel Coronavirus (SARS-CoV-2) COVID-19 Antibody test
How does the COVID-19 Antibody Test work?
Diagram of estimated course of Seroconversion
Omega COVID-19 Antibody Test
This allows for the distinction between antibodies present as a result of infection or from vaccination, as vaccination results in anti-S antibodies only. The N protein assay is qualitative and the S protein, quantitative.
High clinical sensitivity of antibody assays begins from 14 days after infection. Therefore, the timing of this test is important as to when reactivity will occur. Taken too early, the assay may not demonstrate the presence of antibodies.
Clinical specificity of 99.8% and sensitivity of 99.5% was reported after 14 days from PCR confirmed infection for this assay.
Research is lacking as to the duration of persistence of antibodies following infection or vaccination and there is individual variation as a result of factors that are not limited to: immunomodulation as a result of age, medication and co-morbidities. However, antibodies appear to be present in the order of months following infection or vaccination in many individuals.
While the presence of antibodies is likely to confer immunity, the absence of antibodies does not necessarily mean a lack of immunity due to other mechanisms such as the presence of T-cell epitopes which are not measured in this assay.
COVID Testing Program Information
When Should Individuals Be Tested?
- Where an individual had symptoms of Covid-19 but did not have this confirmed with a diagnostic test at the time.
- Where someone may have had asymptomatic infection
- When it is required for travel or occupational risk assessment
- To investigate someone’s immune status from vaccination or infection
How Does Omega Compare
- N-protein antibody negative:
- An individual has not been infected with SARS-CoV-2, or
- An individual has been infected with SARS-CoV-2 in the past, but their antibody levels were too low for the test to detect, or
- An individual has been infected with SARS-CoV-2, but there has not been enough time for antibodies to develop. (Antibody response varies from person-to-person and can take up to 3-4 weeks post-onset of symptoms or post-exposure to be reliably detected. Consideration should be given whether through age, medication, co-morbidities or other factors affecting the immune response that the levels of antibodies may be blunted.
- N-protein antibody postive:
- An individual has been infected with the SARS-CoV-2 virus.
- Rarely (<0.5%) false positive results may be caused by cross-reactivity of the test with other viruses.
- S-protein antibody negative:
- An individual has not been vaccinated
- An individual has been vaccinated but:
- They did not respond to vaccination. Variables to consider would include but are not limited to age, immunomodulation diseases and drugs. The type of vaccine they received and when this was administered.
- They did respond but the immune response is no longer visible as antibody levels have declined.
- S-protein antibody positive:
- The individual has been vaccinated.
- If they are also N-protein antibody positive they may have had the disease only (if no record of vaccination) or have been vaccinated and caught the disease either before or after vaccination. Clinical correlation will help determine which is the case.
- Limitations of COVID-19 antibody testing:
- Positive antibody test results do not gurantee the prevention of re-infection or transmission of SARS-CoV2.
- Antibody results should not be used to diagnose active infection
- Tests performed < 2-3 weeks after onset of symptoms have reduced clinical sensitivity and may lead to false negative results
- Rare false positive results may be due to cross-reactivity with other coronaviruses
- Immunosuppressed individuals or those with mild disease may not produce measurable antibody levels
COVID-19 Antibody Testing : Frequently Asked Questions (FAQs)
How do you test for Covid-19 antibodies? Antibodies are tested from a blood draw that is sent to an Omega lab for processing.
Where can I get the test done? Omega does not collect samples, so the blood draw must be arranged by your Health Care Provider.
When can I get tested for Covid-19 antibodies? The test is done after people have recovered from the infection or have had the vaccine. Antibodies to Covid-19 after infection or vaccination appear within 2-3 weeks. If you are tested too early, the test may not detect antibodies as they will not have been made yet by the body
How long does it take to get the results? Once the sample has reached our lab, results are available within 24 hours.
What will the results tell me? The results will tell you if you have antibodies to Covid-19 from vaccination or infection.
Can the Omega antibody test tell the difference between antibodies from the vaccine and antibodies from infection? Yes. Omega’s antibody test tells you if you have antibodies from the vaccine or from having had Covid-19.
Antibodies are specific to different parts of the virus and fit like a key in a lock. This means we can measure antibodies that have been made against different parts of the virus. This tells us whether your antibodies are because of infection or vaccination. Can antibody testing tell me if I currently have Covid-19? No. Antibody testing cannot tell you if you currently have Covid-19. You need to do a PCR or antigen test if you want to know if you currently have Covid-19.
Why would I get tested for Covid-19 antibodies?
- For travel as some countries require this test before you enter.
- To find out if you had Covid-19 in the past but didn’t get a Covid test at the time.
- To see if you had Covid-19 but had no symptoms.
- You may get a test to see if you could donate blood or plasma.
- To find out if you have antibodies from the vaccine.
How accurate is the Covid-19 antibody test? After 14 days from a confirmed case of Covid-19, our antibody test is 99.5% sensitive and 99.8% specific overall.  This means the risk of a false positive or false negative result is extremely low.
Can you tell which variant of Covid infection I had from antibody tests? No. It is not possible to determine which variant of Covid someone has had from this antibody test.
Are there any risks to taking this test? A blood draw is required and there may be discomfort when this is taken and mild bruising afterwards. Omega labs does not perform blood draws so this must be done through your Health Care Provider.
There is a risk that antibodies are not detected because the test was performed too soon after vaccination or infection. There is a very low risk that even though you have had Covid-19 or been vaccinated, the test is reported as having no antibodies, where in reality there are antibodies (a false negative). There is a very low risk that the test could show you have antibodies where in reality you do not (a false positive). The risk of these errors is <0.5%.
How long do Covid-19 antibodies last after the vaccine or infection?Because research is ongoing, the exact time Covid-19 antibodies last is not known but it is likely to be months to years.
What is the difference between PCR, antigen and antibody tests? PCR and Antigen tests will show if you are currently infected with Covid-19. The antibody test will tell you if you have antibodies to Covid-19 from past infection or the vaccine. 1. Roche. Available from: https://diagnostics.roche.com/global/en/products/params/elecsys-anti-sars-cov-2.html.