COCO and PREVENT study FAQs

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.

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.

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.

There are three possible results of an antibody test:  Positive, Negative or Equivocal.

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.

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.

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.

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.

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.

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.

No. At present, we will only report an antibody test result as being positive, negative or equivocal.

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.

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).

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.

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.

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.

If you have further questions about the antibody result from this study, please do not hesitate to contact the Clinical Immunology Service at clin.imm@nhs.net