Virtus Logo


COVID-19 Quantitative Antibody Testing Service and Swab (PCR) Testing in partnership with Circular 1 Heath

COVID-19 antibody and swab testing

Having quantitative testing is important as it tells you how strong your immune response to SARS-CoV-2 is. It also gives you a baseline measure so you can check whether your levels have changed over time.

Prof. Sebastian Johnston, CMO, VirTus

COVID-19 antibody and swab testing


In response to the COVID-19 pandemic, we have launched our first  COVID-19 serology test – also called an antibody test – which determines whether an individual has previously been infected with SARS-CoV-2, even if they were asymptomatic.

Our first test, which has been CE marked and fully approved, and carefully validated against community-based COVID-19 cases, is available now. There will be further variations of this test to come. Below we summarise some of the science and performance properties of our test and the ways in which it has been validated.

If you would like to purchase one of our testing kits, you can do so online through the VirTus Shop.

If you are interested in finding out more about our testing services for businesses or large groups, please contact us at

Why do we test for antibodies?

Antibodies are proteins that our immune systems produce in response to infectious agents such as viruses. These antibodies identify specific viruses and bind to them, thus blocking them from entering our cells, multiplying and causing symptoms.

If a person has previously been infected with SARS-CoV-2, they are likely to have these antibodies in their blood (in particular IgM and IgG – see figure below). Our test detects both of these antibodies in blood samples and provides some indication of a person’s susceptibility to future infection.

Why is this important?

Many COVID-19 cases (people with symptoms caused by infection with SARS-CoV-2) had only very mild symptoms and some people with SARS-CoV-2 infection had no symptoms whatsoever. Going forward, close monitoring of previous infections will be critical to:

  • Understanding the strength of immunity to SARS-CoV-2 that you as an individual may have
  • Helping employees to return to work more safely, with a better understanding of their own risk of SARS-CoV-2 infection and the risk they may pose to others
  • Gaining a better understanding of a workforce’s susceptibility to infection
  • Understanding the degree of immunity to SARS-CoV-2 within a community.


Key properties of our test

  • This is a quantitative laboratory test that will give a numerical value for the strength of your antibody response (from a level of zero to a maximum value of around 3), this will determine whether an individual has a weak, medium, strong or very strong antibody response to SARS-CoV-2 (or a negative test).
  • This test will establish a baseline level for your antibody response, which will allow you to test again in the future to see if your antibody level is changing over time.
  • This test measures levels of two antibody types (IgM and IgG) against SARS-CoV-2. As some other tests only detect IgG antibodies, this test should detect an additional proportion of people who have IgM antibodies, but have not yet developed IgG antibodies.
  • Our test runs on a form of enzyme-linked immunosorbent assay (ELISA), a commonly used biochemical test that can be used to detect antibodies to many infectious diseases.
  • This works by mixing a small amount of an individual’s blood with a solution containing certain proteins (antigens) from the virus. If antibodies to SARS-CoV-2 are present in an individual’s blood, they will recognise and bind to these viral proteins.


How accurate is this test?

This test has been shown to detect 100% of severe hospitalised cases and 86.9% of 107 milder community cases, including asymptomatic people with a positive SARS-CoV-2 swab test, this is the test sensitivity. Most other tests have not been validated in community cases of COVID-19, nor in asymptomatic people with a positive SARS-CoV-2 swab test.

For high or very high positives, the specificity of our test is 100%. This means for moderate to very high antibody positives, we are almost 100% certain they are not false positives. For moderate level positives, the specificity of our test is 99.5%. This means for moderate antibody positives, one in 200 tests could be a false positive. For low level positives, the specificity of our test is 98.6%. This means for low antibody positives, 1.4 in 100 tests could be a false positive.

Note that in Prof Johnston’s view, a “false positive” is probably more likely to be showing cross-reactive protection from prior seasonal coronavirus exposure, than being a true false positive.


What does my antibody test result mean?

An overall result of “Negative” means that any IgM or IgG antibodies to the SARS-CoV-2 (the virus that causes COVID-19) S1 spike protein that may have been present in your blood sample were not detected by our test. This could be because:

  • You have been infected, but your immune system has produced antibodies that do not bind to the SARS-CoV-2 S1 spike protein in our test
  • You have been infected, but the infection was mild and the antibodies you produced are below the detection limit of our test (if you have had typical COVID-19 symptoms, the first two of our three explanations are the most likely explanations)
  • You have not previously been infected.

Receiving an overall result of “Positive” from our test confirms that you have had COVID-19 in the past and that your immune system has mounted a memory immune response against the virus that is detectable by our test – a positive result for either IgM or IgG gives an overall positive result. For those that are positive, we will also show you whether you have a low, medium, high or very high amount of antibodies to SARS-CoV-2, with a numerical value for your antibody level – indicating the strength of your immune response to SARS-CoV-2.

Obviously the stronger your immune response to the virus the better, but it is Professor Johnston’s belief that even a low positive antibody level in our test is actually evidence that you have a strong immune response to the virus.

This is because the MHRA required all companies developing antibody tests to set their cut-off for a positive test high (to avoid companies giving out false positives). This has resulted in all tests missing antibody responses in milder cases – we missed 13% in our validation cohort of community COVID cases – so the ones we do actually detect are at the stronger end of the antibody response spectrum.

Past experience with seasonal coronaviruses tells us that it is highly likely that the presence of detectable antibodies does confer protection against repeated infections. In one study people who had mild symptoms after they were infected with a seasonal coronavirus, were all protected from having symptoms when they were re-infected with the same seasonal coronavirus a second time one year after the first infection. It is likely that people who developed symptoms with COVID-19 that were more significant than mild, will have developed a stronger immune response and will therefore be protected to a greater degree than the protection seen in the above study with mild symptoms with a seasonal coronavirus.

Are the antibodies that our test detects protective against SARS-CoV-2 infection?

This test has also been tested against a SARS-CoV-2 neutralisation test (details below) and both IgM & IgG antibody levels measured by our test correlate very strongly (r=0.7, P<0.0001) with virus neutralising (blocking viruses from infecting cells) activity.

What do we offer?

We are currently offering this testing service to individuals, businesses/companies, and other organisations in an effort to help bring employees back to the workplace safely. This is via a home finger-prick kit sample kit or professional phlebotomy service, allowing individuals to give their blood samples at home, the workplace or wherever is most convenient.

If testing is carried out at the workplace, employees will need to be sampled sequentially so that social distancing can be maintained. Individual results will normally be returned by e-mail within 1-2 days of us receiving your samples in our laboratory. For companies, a comprehensive company report, indicating the percentage of employees with significant antibody levels, will be delivered within 10 working days.

Personal testing can also be arranged via a number of London based GP practices – those currently offering our test include Dr Georges Kaye, Dr Chiara Hunt, Dr Simon Moore, Dr Peter Kapff, Dr Tim Ladbrooke and Chelsea Medics.

If you would like to purchase one of our testing kits, you can do so online through the VirTus Shop.

Has our test been approved by Public Health England (PHE)?

PHE is not a regulatory body and PHE does not approve tests. PHE do assess testing kits/tests that they wish to use themselves for their public health services, but they do not approve in house tests such as the test we are offering.

Our test has been validated using exactly the same methodology as PHE uses to assess tests it wishes to use, by testing against large numbers of SARS-CoV-2 proven positive samples (in our case community based, as well as hospitalised case samples) and large numbers of true negative samples taken at least 6 months before the first COVID-19 case in the UK. The results of our validation, and those of other tests are below.

To note:

  • Results will be delivered via email within 1-2 days of receipt of samples in VirTus’ laboratory (Camden, London).
  • VirTus’ labs are undergoing accreditation by the UK Accreditation Service (UKAS).


Further VirTus tests available soon:

  1. Additional SARS-CoV-2 proteins

Our current test detects antibodies to the spike (S1) protein of SARS-CoV-2. VirTus are developing further quantitative ELISA tests using other SARS-CoV-2 proteins (including the N protein or nucleoprotein) to pick up additional positive results in people who are negative to our first test. These will include up to four additional SARS-CoV-2 proteins with the hope that close to 100% of people with antibody will be detected. These tests will become available over the next few weeks.

  1. Neutralising antibody test

This test uses a live virus with the SARS-CoV-2 spike protein to see if the antibodies present in people’s blood can stop this live virus infecting cells. This is the most comprehensive test and it will also be available in a few weeks.

Summary of our service compared to other tests:

VirTus Test Other Tests
Quantitative result (numerical value – plus negative, low, medium, high or very high positive) Yes No (Positive/Negative only)
Validated against community-based COVID-19 cases Yes No
IgG and IgM testing Yes No (only IgG or not specified)
Sensitivity in community-based COVID-19 cases 86.90% ?
Sensitivity in hospitalised COVID-19 cases 100% 100%
Specificity 98.4 – 100% 99.5-100%
Virus protein tested against S1 (spike) N (nucleocapsid)
Validated against a virus neutralising assay Yes No
Results in 1-2 days Yes Yes


Having quantitative testing is important as it tells you how strong your immune response to SARS-CoV-2 is. It also gives you a baseline measure so you can check whether your levels have changed over time.

Prof. Sebastian Johnston, CMO, VirTus

Would you like to purchase our COVID-19 Antibody Test?

You can now order your home sample kit with FREE Next Day Delivery.


Get in touch

Would you like to know more about our COVID-19 antibody testing service? Please do get in touch.