Antibody testing after Covid-19 vaccination

Should I have an antibody test?

Antibody tests to check your response to COVID-19 vaccination are not routinely available on the NHS, unless you are admitted into hospital with COVID-19, when an antibody test is taken to see if you are eligible for passive monoclonal antibody therapy. There are companies that offer private antibody tests.  It is a personal decision whether you choose to pay for private antibody testing.  Some people have reported to us that having the knowledge of their antibody response after vaccination helps them deal with the risk of COVID psychologically. 

This article gives a few things to consider before deciding whether to pay for a test.

What does testing involve?

Many of the tests are available by post. They involve pricking your finger with a small needle and collecting a few drops of blood in a tube. You send the blood sample to a lab to be analysed. It is important to note that different antibody tests measure different things.

What are the differences in the tests available?

The antibodies your immune system makes if you have had COVID-19 in the past are not the same as the antibodies your immune system makes after you have been vaccinated.

Some tests only check for antibodies from previous infection. These are sometimes called an 'anti-N' test because they test for antibodies that react to a part of the coronavirus called the nucleocapsid.

Some tests check for antibodies from either previous infection or vaccination. These are sometimes called an 'anti-S' test because they test for antibodies that react to the spike protein. Some tests check for anti-N and anti-S antibodies.

If you decide to get an antibody test, make sure you order one that is testing the right thing. Check the test information. It should say if it measures antibodies from vaccination or from previous infection. It might say what antibody it checks (anti-S or spike antibodies for vaccination response).

It is also important to remember that antibody levels change over time. It usually takes 2 to 4 weeks after vaccination for antibody levels to peak and then they gradually go down.  Scientists do not know yet how long the antibody response to vaccination lasts, or how this relates to your overall protection from COVID-19.

Remember antibodies are only one part of your immune response to vaccination

Different COVID vaccines work in different ways, but they all aim to train your immune system to recognise and remember coronavirus. Two main types of cell are important in your immune response to vaccination: B cells and T cells.

Some B cells respond by making antibodies straightaway. Some B cells do not make antibodies straightaway but are programmed to remember the virus so they can make lots of antibodies quickly if they come across it again. These are called memory B cells.

Some T cells respond by making substances that aim to kill the virus. Some T cells respond by activating B cells and telling them to make lots of antibodies. Some T cells are programmed to remember the virus so they can respond quickly if they come across it again.

Antibody tests check whether or not your B cells made antibodies straightaway in response to vaccination. They do not measure your memory B cells or test whether your T cells have responded.

T cell responses are much harder to measure than antibodies.

Tests of T cell response are not routinely available, either on the NHS or privately, although they are used in some clinical trials.

What will the results mean?

Scientists do not know yet what antibody test results mean in terms of your protection against COVID.

Some antibody tests tell you if you have made antibodies or not, but do not tell you how many you have made. You might get a positive result even if you have made very few antibodies. Other tests measure the exact level of antibodies you have made.

Dr Matthew Buckland, Chair of Immunodeficiency UK's Medical Advisory Panel says

'At the moment, scientists/clinicians don't know how antibody levels relate to a person's overall protection from COVID-19.  Low antibody levels might still offer useful protection, while normal antibody levels do not guarantee complete protection. Having a negative antibody result doesn't necessarily mean you haven't responded to vaccination - you might have a T cell response that may provide some protection.  Antibody testing does not measure this T cell response.

With respect to testing it should be clear that since there is no single unified testing platform you cannot say what level of antibody is normal or abnormal and there is been no correlation with the level of antibody level and protection against disease. We just don't have this knowledge yet and this requires further research.'

Will the information help me informed decisions about my risk level in relation to Covid?

Healthcare professionals base their advice on your individual circumstances, not your antibody response. This is because, regardless of your antibody levels, your medical team base their advice on your individual circumstances. When they recommend steps you should take to reduce your risk from COVID-19, they consider factors such as:

  • your age
  • your type of immunodeficiency and any other illnesses you have
  • what treatments you have received or are taking
  • the level of COVID-19 infection in your area
  • how much contact you have with other people at home, socially and at work
  • your personal risk of becoming severely ill if you do get COVID-19
  • your mental wellbeing.

Dr Matthew Buckland, comments 'Most patients with immune deficiency reported a general improvement in respiratory health and reduction in infections during periods of lockdown and when social distancing was being widely observed.  Sensible precaution (hands, face, space) during the winter months remains the most useful measure against all respiratory viruses and bacteria during the cold and flu season, irrespective of someone's level or presence of COVID antibody.'

I do want to go ahead with testing my vaccination response. Can Immunodeficiency UK recommend a private testing company?

Immunodeficiency UK cannot recommend suppliers of private tests. Please note, as above, different antibody tests measure different things so make sure you order the right test. If you decide to go ahead find out that the test is being done in an accredited lab (UKAS accredited to ISO15189), which is the standard for verified laboratory tests.

Posted 9th November 2021. Approved by the Chair of the Medical Advisory Panel