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HOW USEFUL IS A COVID ANTIBODY TEST?

It’s getting a bit confusing…not to mention tedious…trying to work out the difference between all of the different Covid tests.

Covid rapid antigen test (RAT test), Covid PCR test, Covid lateral flow test (LFT), Covid lamp test….if you are still unsure about the differences (or even care!) you can read more here.

Then there’s the fit to fly test and the day 2 lateral flow test. Covid travel tests are changing again as this latest article describes.

And now, just when we were starting to get our heads around all those, we are seeing more and more about the Covid-19 antibody test too.

But do you need a Covid antibody test and what does it mean?

What is a Covid antibody test?

Unlike the rapid / lateral flow antigen test, the PCR test or LAMP test, which aim to identify current infection, the Covid antibody test can show evidence of past infection or response to vaccination. There are two types of antibody test IgG/ IgM and those for IgG neutralising antibodies of the spike protein.

What’s the difference between an antibody and an antigen test?

An antigen test tells you if you have current infection and requires a swab from your throat and nose (nasopharyngeal or anterior nasal) You need this type of sample because this is where the antigen (virus) will be found. An antibody test will tell you if you have antibodies, which your immune system will have produced from either being infected or from vaccination. There are different types of antibodies, and the BioSURE COVID-19 IgG Antibody self-test only detects neutralising antibodies, which are the type of antibody that give you protection. You need to use blood for an antibody test as this where antibodies are found.

What are neutralising antibodies?

Neutralising IgG antibodies are the antibodies that target the spike of the SARS-CoV-2 virus so that it cannot enter the cell it is trying to infect and therefore the virus cannot replicate. They can also help stop the virus from changing, which are known as conformational changes that help it improve how it enters and replicates within a cell.  They are different from binding antibodies which they work alongside with, which bind to the virus and then alert your immune system so it can produce white blood cells to fight the virus off. Neutralising antibodies are made by B-cells which are made in your bone marrow.

When you have an infection, your body’s immune system produces antibodies. One function of antibodies is to bind to the viral particles as red flags, that prompt other cells in the body to destroy them. Other antibodies are neutralising – they can bind to the virus in such a way as to deactivate them without the need for back-up…perhaps by preventing the virus from entering our own cells. In SARS CoV-2 infection, it is the spike protein that seems to be the key area to block, to stop the virus getting in.

What is the difference between the BioSURE COVID-19 IgG Antibody self-test and other antibody rapid tests that are available?

Firstly, other antibody rapid tests that are available are not CE marked for self-testing. Secondly, there are two main different types of antibodies – nucleocapsid antibodies (which appear after an infection) and spike antibodies (which appear after an infection or vaccination) which are the neutralising IgG antibodies – the ones that are important for you to know your status about. Most antibody rapid tests, only detect the nucleocapsid antibodies which you do not produce from vaccination. The BioSURE IgG Antibody Self-Test detects the IgG spike antibodies that bind to the SARS-CoV-2 spike protein, which is the part that the virus uses to infect human cells. This is why they are called neutralising antibodies. The BioSURE COVID-19 IgG Antibody self-test holds more significance owing to the neutralising capabilities of IgG antibodies (as opposed to detecting antibodies to the Nucleocapsid protein).

If your immune system is working well, you should see levels of various antibodies rising at different intervals after infection, as these defences kick in.

What about the Covid vaccine?

The idea of a vaccine is to trick the body into thinking we have had an infection, and so to start producing these antibodies, which can then spring into action if we do actually get exposed to Covid. We can then avoid getting infected – or at least fight it off more quickly, with a less severe attack.

How long do Covid antibodies last?

Unfortunately, though, after infection or vaccination, the antibody levels seem to drop off after a few weeks or months. This rate varies from person to person. How much that matters is still unclear, as the body has a second line of defence. It produces a number of immune cells with memory….meaning that they can respond more quickly to an infection they have seen before, hopefully nipping it in the bud. How good our immune system’s memory is for Covid, though, remains to be seen.

What can a Covid antibody test tell me?

It seems that about 30-70% of people will produce antibodies after a single shot in a double vaccine programme, rising to 98% or more after the second dose. Interestingly, men are slightly less likely than women to show a response.

If you have a positive Covid antibody test, especially if it is a specific neutralising antibody test, it suggests you are less likely to catch Covid or to have a severe attack if you do. Vaccines have reportedly prevented over 46,000 hospitalisations and saved over 30,000 lives by stimulating antibodies to the virus.

A positive test provides reassurance that a severe infection is unlikely – though shouldn’t mean you throw caution to the wind, of course. If you have a negative antibody test, it doesn’t necessarily mean that you have no immunity to Covid as the test doesn’t identify all the defences. But it may mean you take even more care.

There is also a lot of debate about providing vaccine booster shots to people who may already have antibodies, when there are many people in the world who haven’t even had their first dose yet. Not only does this raise ethical issues, but it risks the virus circulating for longer in our communities. This potentially increases the threat of new variants emerging, which may be less susceptible to current vaccines. That’s to the detriment of all of us.

So, whilst Covid antibody tests are raising many questions as well as answers, they provide us with more information to help us navigate our way through this pandemic. And, the more information, the better.

Where can I book a Covid antibody test?

If you’d like to find out about your own antibody status after infection or vaccination, you can use one of our antibody self-tests, at home. If you’d like online support from our specialist nurse please add a supervision appointment to your basket too.

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