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Explains antibody testing for COVID-19 including that it cannot tell people whether they are immune.

First published:
29 June 2020
Last updated:

What is COVID-19 Antibody testing?

COVID-19 antibody tests are used to find out whether a person has previously had the virus.

The antibody test works by taking a blood sample and testing for the presence of antibodies. Antibodies are produced by the body in response to an infection and can usually be found in the blood after around 2 weeks following infection.

Antibody tests are different to antigen (swab) tests which are in widespread use across Wales to see if you currently have the virus. Antigen testing continues to play a critical role in controlling the spread of the disease in Wales. Once people know they currently have the virus, they self-isolate and work with the NHS Test Trace Protect team to make sure their contacts don’t spread the virus either.

The value of antibody testing

Antibody testing will identify whether people have had the virus or not. Antibody testing will help build a picture of how many people have had infection, and how far and wide the virus has spread in Wales.

What antibody testing cannot do is tell people whether they are immune to catching the disease or infecting other people.

As COVID-19 is a new infection, we don’t yet know enough about how effective antibodies are at getting rid of the virus, whether they will protect you from getting it again, or whether having antibodies means you cannot pass the virus on to others. We also don’t know how long the antibodies will last. As the scientific evidence grows, we hope to have the answers to these questions.

Even when you know you have had the virus, the only way to reduce the risk of you becoming ill, or passing the disease on to others you care about, is to follow the latest government advice on controlling the spread of the virus. So even with a positive antibody test, to protect the people you care about and play your part in keeping Wales safe. You will still need to practice social distancing, wash your hands well and often, get a test (swab) if you have symptoms, and self-isolate if you have the virus or if you are a contact of someone who has the virus.

Types of antibody tests

There are two types of antibody test. Both require a blood sample and currently need to be carried out by trained staff.

The laboratory assay test, where a sample of blood is tested in a lab, has now been approved for use, and in Wales we are working on a four nation basis to make sure we have the lab tests we need.

The finger prick antibody test (lateral flow test) is currently being verified in Wales to make sure it performs well. It is anticipated that this work will be completed shortly. There is also work ongoing to decide if this type of test could be suitable for use at home. We will provide more detail on the development of this type of test as work progresses.

We will also continue to work closely with Public Health Wales, Life Sciences Hub Wales and the private sector to look at all options for testing for antibodies and to scan the market for new tests.

Prioritisation of antibody testing

Antibody testing is only available to priority groups at the moment. If you are not in one of these priority groups and have not been invited for a test, please do not contact your Local Health Board to request an antibody test at this point in time.

At present, testing will be prioritised for:

  1. a sample of the school staff who have worked in the education hubs providing support to children of key workers and vulnerable children during the pandemic
  2. healthcare workers, with priority given to those who have potentially been repeatedly exposed to the virus

Clinicians will also be able to request the tests for patients in hospital settings if they think it’s appropriate.

For healthcare and teaching staff, their employers will work with the local health boards to determine when and who will be invited for testing as part of this programme. Tests will not be conducted at the request of the individuals, and health care workers and teaching staff should refer to their employer for information.

There are benefits in knowing whether the teaching staff working in the education hubs and healthcare workers have had the virus, and in collecting data on the test results. Understanding patterns of infection will help point to areas in these settings which could target enhanced infection prevention and control to help reduce the spread of the virus. The information obtained will also be used to inform the expert group in the development of our approach to the best use of antibody testing in Wales in the future.

An updated testing plan will be published soon, bringing together the role of antigen and antibody testing, and will provide an important framework for supporting the delivery of Wales’ Test, Trace, Protect strategy.

What a positive antibody test result means

If you have had an antibody test for COVID-19 and it is positive, it means you have probably had the virus (novel coronavirus) that causes COVID-19, and have produced antibodies against it.

A positive antibody testing does not tell you that you are immune to catching the disease or that you cannot infect other people

Even when you know you have had the virus, the only way to reduce the risk of you becoming ill, or passing the disease on to others you care about, is to follow the latest government advice on controlling the spread of the virus.

So even with a positive antibody test, to protect the people you care about and play your part in keeping Wales safe and protecting the recovery, you will still need to practice social distancing. You should also wash your hands well and often, get a test (swab) if you have symptoms and, self-isolate if you have the virus or if you are a contact of someone who has the virus.

What a negative antibody test result means

If your antibody test is negative, it means that the laboratory reviewing your sample has not detected antibodies to the virus that causes COVID-19 in your blood. There could be a number of reasons where negative result could mean that you:

  • have not been exposed to the virus that causes COVID-19
  • have been exposed but are in the time period before an antibody response could be generated by your body
  • have levels of antibodies too low to be detected, for example because you had a recent infection and haven’t produced antibodies yet, or because you had the infection a long time ago, and the antibody levels have dropped

What an inconclusive antibody test result means

If your antibody test is termed as ‘equivocal’, it means that the result is inconclusive.

What else you need to know

Despite the outcome of an antibody test, if you become symptomatic for COVID-19 at any point (fever, cough, altered sense of taste and smell), then you must apply for an antigen test and self-isolate until the results are known. You must continue to self-isolate from onset of symptoms for 10 days if your swabs results are positive whilst household members should isolate for 14 days.

If you fall within one of the 2 priority groups for antibody testing, you will be expected to sign a disclaimer before your blood test is taken. This is to ensure that you have understood what the results of the test will mean (i.e. that although you have antibodies, you are not exempt from Government advice on social distancing, you are not necessarily immune to reinfection, and you may still pass on the virus to others). If after having discussions with the healthcare worker you do not wish to have the test then you can refuse. All antigen and antibody test results will be available to medical health practitioners via your medical record.

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