The latest government data suggests that so far more than 39.4 million people have received the first dose of the COVID-19 vaccine which equates to 74.9% of adults in the UK; 48.9% of the adult population have also had their second dose which is an incredible achievement. On 8th June 2021 there were 13 deaths reported within 28 days of a positive test in the UK compared to 55 a year ago showing just how far we have come in the fight against COVID-19.
There are three types of test for coronavirus:
1) A PCR swab test to find out whether you currently have coronavirus. This is a throat and nasal swab, is used in symptomatic individuals and also for travel purposes.
2) A lateral flow test helps to find cases in people who may have no symptoms but are still infectious and can give the virus to others. This is also a throat/nasal swab used in asymptomatic individuals. If positive, a PCR test is required.
3) An antibody blood test (either a capillary/fingerprick or venous sample) which is used to find out whether you have either previously had coronavirus and developed some degree of immunity, or, if you have had the vaccine and raised an immune response.
What are antibodies?
Antibodies are proteins used by the immune system to identify and neutralise harmful objects e.g. viruses. When a virus like SARS-CoV-2 coronavirus enters the body, cells called B lymphocytes create antibodies to protect you, and these antibodies remain to defend against the virus if it comes back. Vaccines teach your body to mimic this response without you actually becoming unwell. This is why you develop antibodies both after natural infection with a virus and after getting a vaccine.
What can the tests tell me?
Most of these tests detect antibodies to one of two types of protein from the coronavirus:
– Nucleocapsid (N) protein
– Spike (S) protein
If you were to get infected with SARS-CoV-2, your body would make antibodies in response to multiple viral proteins, including the nucleocapsid and spike proteins.
The vaccines currently authorised for use in the UK trigger antibodies against the spike protein, so an antibody test after you get the vaccine should only detect antibodies to that spike protein, not to the nucleocapsid protein.
If you had a COVID-19 infection, both the nucleocapsid and spike protein tests would be positive because you have been infected with the whole virus.
Some tests look for antibodies to both the spike protein and the nucleocapsid protein to distinguish between vaccination and infection.
Certain tests look for specific antibodies to these proteins, depending on how long it has been since you were infected or vaccinated: IgG and IgM antibodies.
What are the differences between IgG and IgM?
IgM (immunoglobulin M) antibodies are found in the blood and lymph fluid and are the first type of antibody made as a response to an infection. They prompt other immune system cells to eliminate foreign substances. IgM antibodies make up about 5 -10% of all antibodies in your body.
IgG (immunoglobulin G) antibodies are found in all body fluids and are the most common, making up 75 -80% of the antibodies in your body. They are very important in fighting viral infections.
IgG tend to be longer-lived and are typically the antibodies that are tested for in the clinical and research setting to look at long-term protection or immunity. IgM is more often seen early in infection or early after vaccination.
It is well known that IgG (and immunity levels) do reduce in the months after infection and this test will enable you to monitor your IgG levels over time if you would like to monitor this.
What are the different antibody tests offered by Preventicum?
At Preventicum we are delighted to be able offer our clients the opportunity to have an antibody test to identify past infection with COVID-19 and/or response to SARS-CoV-2 vaccinations. The two tests available are developed by Roche and VirTus.
Both tests detect antibodies developed in response to the vaccines currently in use in the UK. They utilise the receptor binding domain of Spike antigen. This is different to the older antibody tests that looked at the antibody response to the nucleocapsid protein and was targeted at immune response after infection. These older tests cannot detect the antibody response following a vaccination.
The Roche test gives the quantitative result for the total antibodies. The result is considered positive if it is >0.8.
The VirTus test gives the quantitative results for both IgG (long-term antibodies) and IgM (short-term antibodies). This test also provides an interpretation as to whether levels are very high, high, medium or low.
‘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.’ Professor Sebastian Johnston, CMO, VirTus
How accurate the tests?
Roche sensitivity is 99.98% and specificity 98.8%.
VirTus sensitivity 86.9% (community samples) & 100% (hospital samples) and specificity 98.1%
What is the difference between a quantitative test and a qualitative test?
Some antibody tests are qualitative, which means they will simply give you a positive or negative result for antibodies rather than an actual level. Others are quantitative, which means they provide an actual antibody level, or titre.
Up until recently antibody tests simply gave positive or negative results, these new advanced tests provide numerical results to give you the level of COVID-19 specific antibodies in your blood, which further enhances understanding of the level of your antibody response.
The SCOV and VirTus blood tests that we offer are both quantitative tests which gives more in depth information around your antibody response.
What does an antibody result mean and does this affect what I can do?
There are three possible results after taking an antibody test: positive, negative or indeterminate (borderline).
A positive result means that COVID-19 antibodies have been found in your blood, which indicates that you have previously been infected by coronavirus or received the vaccine. This does not mean that you are immune to coronavirus.
We still do not know how much immunity we get from a COVID-19 infection or the vaccination so even if the antibody result is positive it is possible that one could be infected a second time or carry and transmit the virus to infect others. We also do not yet know how long this immunity lasts for, immunity to other coronaviruses can wane quickly. Current data indicates that a positive antibody result can protect against COVID-19 for at least 6 months.
If the test gives you a negative result, it means that you do not have the antibodies to indicate that you have had coronavirus so it is less likely that you had had COVID-19, or this is linked to your T cell response.
You can also have an indeterminate result, meaning that the test cannot confirm either a positive or negative result. If this is the case, we would recommend that you repeat the test again in a couple of weeks’ time.
At this stage there is no formal guidance to identify how antibody levels correlate with immunity. We do not know if an individual with a positive result showing presence of IgG levels following being infected with SARS-CoV-2 will be protected, either fully or partially from future infection, or for how long protective immunity may last.
Due to this, regardless of antibody test results our behaviour should continue in line with the government guidance around social distancing, hand washing and the use of PPE.
What if I have no antibodies?
It would be rare to have no antibodies after receiving the vaccine, but it is important to recognise that the COVID-19 vaccine may confer protection that goes beyond antibodies. We also generate T cell immunity and it is thought the vaccinations also causes a T cell response in the body. This is not as easily tested.
Regardless of the outcome of antibody testing it is imperative to continue to follow government guidelines on distancing, hand washing and wearing masks.
When can I have the antibody test?
Testing can be undertaken from 14 days following exposure, onset of symptoms or post-vaccination. The incubation period of COVID-19 ranges from between 1 to 14 days, with the majority of cases manifesting with symptoms at 3–5 days. We would recommend testing after 21 days.
Where can I have the antibody test?
This can be done on the day of your Preventicum health assessment. We can also provide postal options for capillary samples.
How much does an antibody test cost?
The Roche test costs £100
The VirTus test costs £260
When do I get my results?
The Roche test takes 1 working day from receipt at the laboratory.
The VirTus test takes 2-3 working days from receipt at the laboratory.
For more information on our COVID-19 antibody tests, please email info@preventicum.co.uk or call 020 7605 6900
