COCO and PREVENT study FAQs
Many thanks for participating in either the COCO or PREVENT study. As part of these studies you may have received the result of an antibody test. We have had lots of enquiries about our studies and the results of the antibody test.
As a result, we have provided some answers to our frequently asked questions (last updated 23/6/2020).
Antibodies are protective proteins produced by the immune system in response to infections. We are particularly interested in the antibody response against SARS-CoV-2, the virus that causes COVID-19.
What is an antibody test?
An antibody test tells us whether or not you have antibodies in your body. These tests normally involve taking blood to find out whether your immune system has responded to infection with the virus COVID-19. We are also interested in whether antibodies can be detected in other bodily fluids such as saliva and capillary (finger-prick) blood. The reason for this is that saliva and finger prick tests would make it easier to test lots of people.
Who is an antibody test for?
The antibody test works best for individuals who have had an illness that is likely to be COVID-19 and where it is at least 14 days since they developed symptoms.
What are the possible results of an antibody test?
There are three possible results of an antibody test: Positive, Negative or Equivocal.
I have received a positive antibody test - what does this mean?
A positive antibody result suggests that you have been exposed to the SARS-CoV-2 virus and your immune system has mounted a response against it. We do not yet know whether this means that you cannot get COVID-19 again and you are immune. We also don’t know how long this immunity will last.
In a very small number of cases, a positive result may be a false positive. This is when you have a positive test but you haven’t actually had COVID-19. It may be due to interference by other viruses or some other factor we don’t yet know about.
Because there are so many unknowns around antibody testing, it is important to note that the result of your test cannot be used to change how you approach social distancing, hand washing and use of personal protective equipment.
Does a positive antibody test mean I am immune to coronavirus?
No. A positive test only means that your immune system has mounted a response against the virus. We are unable to say with any certainty whether this means that you are immune from re-infection with coronavirus.
Does a positive antibody test mean I have the virus and can pass it on to others?
No. An antibody test cannot tell you whether you have the virus at this moment in time or whether you are infectious to others. You would require a swab test for this. It only tells you whether your immune system has made a response against the virus. If you have symptoms of coronavirus, then you should follow the government advice, self-isolate and book a test
I have received a negative antibody test - what does this mean?
A negative antibody result suggests that you have not yet been exposed to the virus. The other possibility is that you have been exposed to the virus and your immune system did not mount an antibody response against it – we don’t know yet how often this happens but it is likely to be highly uncommon. The final reason your antibody test may be negative is that the test is not sensitive enough to pick up the antibodies in your case – our data suggests that this only happens in less than 2% of results.
You should not change your behaviour (including the wearing of PPE, social distancing and hand hygiene) on the basis of a negative antibody test result.
Does a negative antibody test mean I don’t have the virus?
No. An antibody test cannot tell you whether you do or do not have the virus at this point nor whether you are infectious to others. It only tells you whether your immune system has made a response against the virus. If you have symptoms of coronavirus, then you should follow the government advice, self-isolate and book a test.
I have received an equivocal antibody test - what does this mean?
An equivocal antibody results means that we are unable to conclusively tell whether your result is positive or negative. This occurs in approximately 1-2% of cases. It might be because you have very recently had COVID-19 and have only just started to produce antibodies against the virus. If you contact your local study team, they may be able to offer you the opportunity to repeat this test, two weeks after your first test to provide further clarity.
You should not change your behaviour on the basis of an equivocal antibody test result.
Can you tell me how strongly positive or negative my result was?
No. At present, we will only report an antibody test result as being positive, negative or equivocal.
Is it possible that my positive result could have been caused by another coronavirus?
It is possible, but highly unlikely. As far as we can tell, the test that we perform in our laboratory is highly specific in identifying antibodies to SARS-CoV-2 (97.8%). In real life, no test can be 100% specific, so there is a small possibility that the test might have returned a positive result due to another factor interfering with the assay.
How accurate is the antibody test?
Our studies have found that the test is 100% sensitive in people who have been hospitalised with proven COVID-19 disease. In people that have had a milder disease the test is 98% sensitive in detecting antibodies. The test is 97.8% specific which means that 2.2% of samples may incorrectly be called positive (these statistics are correct as of 09-06-20).
I have had another antibody test done in another laboratory and the results are different from those from this study. Why might this have occurred?
There are different antibody tests that detect antibodies against different parts of the virus and work in slightly different ways. No comprehensive comparisons of the performance of antibody tests produced by different manufacturers has been undertaken, although, for accredited medical laboratories such as ours, a nationwide effort is underway to help better understand the results arising from different types of test.
Can you tell me what the results of my saliva or capillary blood (finger prick) antibodies are?
No. At present, we are only reporting the results of the tests which have used venous blood as the sampling fluid. Our tests using saliva and capillary blood remain in the early stages of development.
What other tests are available for COVID-19?
There are other tests that detect the presence of the COVID-19 virus itself. The most common of these tests is called a PCR test (this is sometimes called a molecular test or an antigen test in the media). These types of tests are usually done following a nasal/throat swab. They test whether you currently have the virus, and whether you are infectious at the time the test is taken. A PCR test is quite different to an antibody test.
What do I do if I have further questions?
If you have further questions about the antibody result from this study, please do not hesitate to contact the Clinical Immunology Service at firstname.lastname@example.org