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COVIDENCE UK

Antibody FAQs

Here are some answers to common questions about the COVIDENCE UK antibody tests

Negative antibody test result

I haven’t had any doses of the COVID-19 vaccine yet 

Your negative antibody test result suggests that you have probably not been infected with the SARS-CoV-2 coronavirus in recent months.
 
 If you definitely had COVID-19 in the past, and your antibody test is negative now, it might be that your antibody response has faded or ‘waned’ since your illness. This is more common in people who have had relatively mild COVID-19. Immunosuppressant medications or medical conditions affecting the immune system can also dampen the antibody response to coronavirus.

I have had one or more doses of COVID-19 vaccine, and I did my fingerprick antibody test BEFORE, or on the same day as, my first dose of vaccine 

Your negative antibody test result suggests that you were probably not infected with the SARS-CoV-2 coronavirus in the months before you were vaccinated.
 
 If you definitely had COVID-19 before you were vaccinated, it might be that your antibody response faded or ‘waned’ between the time of your illness and the time when you did the fingerprick antibody test. This is more common in people who have had relatively mild COVID-19. Immunosuppressant medications or medical conditions affecting the immune system can also dampen the antibody response to coronavirus.

I have had one or more doses of COVID-19 vaccine, and I did my fingerprick antibody test one or more days AFTER my first dose of vaccine 

Vaccination should stimulate an antibody response, which would be detected by our test. However, there are a few reasons why your antibody test might be negative even though you have had a COVID-19 vaccine:

  • You might have done your fingerprick test very soon after getting the vaccine – so your body didn’t have time to mount an antibody response yet.
  • You might have done your fingerprick test a long time after getting the vaccine – so your antibody response might have faded
  • You might be taking medicines that suppress the immune system – they could interfere with your body’s ability to mount an antibody response after vaccination
  • You might have a medical condition that affects the immune system’s ability to respond to vaccination.


 It’s important to remember that our test only detects one part of the protective response to the coronavirus – the B cell response. Vaccines also stimulate protective T cell responses, which aren’t picked up by our test (you need a fresh blood sample to detect them, so a dried blood spot can’t be used). It may be, therefore, that the vaccine is still giving you protection even if your antibody test is negative.

I do not know whether I have had the COVID-19 vaccine yet (e.g. because I am taking part in a vaccine trial, and I haven’t yet been told whether I was given vaccine or placebo [ dummy injection]) 

Vaccination should stimulate an antibody response, which would be detected by our test. There are a few reasons why your antibody test might be negative even though you took part in a COVID-19 vaccine trial:

  • You might have done your fingerprick test very soon after getting the vaccine – so your body didn’t have time to mount an antibody response yet.
  • You might have done your fingerprick test a long time after getting the vaccine – so your antibody response might have faded
  • You might be taking medicines that suppress the immune system – they could interfere with your body’s ability to mount an antibody response after vaccination
  • You might have a medical condition that affects the immune system’s ability to respond to vaccination.
  • You might have received placebo or dummy injection rather than vaccine as part of the clinical trial protocol. (Vaccine trials can only give useful information if some people receive placebo – otherwise there is nothing to compare the vaccine with).

Positive antibody test result

I haven’t had any doses of the COVID-19 vaccine yet 

Your positive antibody test result suggests that you have probably been infected with the SARS-CoV-2 coronavirus at some time in the last few weeks or months. The presence of antibodies does not guarantee immunity to COVID-19 in the future, so you should continue to follow government guidance to minimise your risk of future infection. The presence of antibodies does not remove the need for vaccination, which is likely to offer additional protection over and above that provided following natural infection.

I have had one or more doses of COVID-19 vaccine, and I did my fingerprick antibody test BEFORE, or on the same day as, my first dose of vaccine 

Your positive antibody test result suggests that you were probably infected with the SARS-CoV-2 coronavirus before you were vaccinated. Government guidance is that people who are offered the vaccine should have it, even if they had COVID in the past – so you should rest assured that were given the vaccine appropriately.

I have had one or more doses of COVID-19 vaccine, and I did my fingerprick antibody test one or more days AFTER my first dose of vaccine 

Your positive antibody test result shows that your body has mounted a successful immune response to the SARS-CoV-2 coronavirus following vaccination. The presence of antibodies does not guarantee immunity to COVID-19 in the future, so you should continue to follow government guidance to minimise your risk of future infection. 

I do not know whether I have had the COVID-19 vaccine yet (e.g. because I am taking part in a vaccine trial, and I haven’t yet been told whether I was given vaccine or placebo [ dummy injection]) 

Your positive antibody test result shows that your body has mounted a successful immune response to the spike protein on the SARS-CoV-2 coronavirus. This could be as a result of vaccination against COVID-19, or as a result of ‘natural infection’ with the SARS-CoV-2 coronavirus. You will not be able to tell which until you find out whether you received vaccine or placebo [dummy injection] in your clinical trial.

General antibody FAQs

If I've had a positive antibody test, can I still get vaccinated?

Yes, the vaccine can be given if you have had a positive antibody test.

I would like to get an antibody test via the COVIDENCE study – is this possible?

Our first round of invitations to have antibody testing have all gone out now, but we are planning a second wave of antibody testing in Summer 2021. If you would like to be invited to have an antibody test in the future, please sign up to take part in the COVIDENCE UK study at www.qmul.ac.uk/covidence

Where can I find out more information about the antibody test used in the COVIDENCE study?

More information is available here and here.

I don’t think I had COVID-19, but my antibody test result was positive. Are false-positive results possible?

False-positive results are rare: just 0.7% of people who did not have COVID-19 had a positive antibody test (more information here).

It is not uncommon for someone to have asymptomatic SARS-CoV-2 infection, and this a more likely explanation for a positive test in somebody who never had COVID-19 symptoms.

I definitely had COVID-19, but my antibody test result is negative. Are false-negative results possible?

Yes, but they are not common: just 3.7% of people who had mild or moderate COVID-19 had a negative antibody test afterwards, using this test (more information here). Most often this arises because the COVID-19 occurred several months prior to the antibody test; we know that antibody responses can wane over a period of months.

Does having the COVID vaccine affect antibody test results?

Yes: we would expect somebody who has had the vaccine to have a positive antibody test within a few days of vaccination.

How will antibody test results from vaccinated people be used in the analysis?

We will use test results from vaccinated people to investigate factors influencing the response to vaccination, and to determine the extent to which having antibodies after vaccination can protect against subsequent risk of COVID-19.

Will my GP be informed about my antibody test result?

No, we are not forwarding results to participants’ GPs. This is because the antibody test is currently being used as a research test only.

How will antibody test results from unvaccinated people be used in the analysis?

Antibody test results from unvaccinated people tell us about whether or not a person had ‘natural’ infection with SARS-CoV-2. This information will be used in our analysis of risk factors for COVID-19.

I don’t want to use my kit – can I give it to somebody else?

No - please do not give your kit to someone else. Your blood spot card bears a barcode that will link the result to your questionnaire data in the COVIDENCE database. If the test result is from somebody else, this will introduce inaccuracies in our data and compromise the scientific value of our study.

I don’t want to use my kit – what should I do with it?

Please post it back to us unused in the pre-paid envelope provided. Please do not give it to somebody else to use.

Is COVIDENCE UK planning further rounds of antibody testing in future?

Yes: we have applied for funding to do another round of antibody testing in Summer 2021.

I sent back my blood spot sample a while ago, but I am still waiting for a result. What is going on?

Unfortunately turnaround times are longer than anticipated, due to pressures on our laboratory arising as a consequence of the pandemic. We are doing our best to get your result to you as soon as we can: thank you for patience and understanding during this very challenging time.

My antibody testing kit was damaged and/or missing one or more components when I received it: what should I do?

Please email covidence@qmul.ac.uk and we will send you a replacement.

I am worried that the blood spots on the card were too few / too small to be useable: what should I do?

As long as there is at least one small blood drop on the card, we will do our best to get a result from it. Please post it to us and we will get back to you to offer another kit if the sample is too small to use.

I was unable to get any blood onto the card, but I still want to take part: what should I do?

Please email covidence@qmul.ac.uk and we will do our best to help, sending a replacement kit if necessary.