SUPERMARKET CHAIN LIDL made headlines last week when it announced it will begin stocking rapid antigen testing kits in its stores.

It prompted public health officials like Chief Medical Officer Dr Tony Holohan to sound a warning about using these kits, which are less reliable than PCR tests. 

While Government acknowledges that antigen testing is an additional measure in combating Covid-19, it is not a substitute for following public health advice, Holohan said. 

No test – PCR or antigen – is 100% accurate. 

Unlike PCR, antigen tests work more effectively if a person is symptomatic but are not as effective at identifying pre-symptomatic cases. 

An antigen test won’t confirm if a person without symptoms has Covid-19 as these tests rely on a high viral load to identify presence of Covid-19. 

According to the HSE, antigen tests are about 80% accurate if a person is symptomatic but only about 50%-60% accurate if a person has no symptoms and self-administers an antigen test.

If a person is symptomatic and receives a negative antigen test result the advice is that they should also get a PCR test, which can also detect early infection in a person. 

The Department of Health advice is clear on this – it does not currently advise the use of antigen tests by the general public, according to a spokesperson. 

Furthermore, if a person gets an antigen test from a private company and tests positive this will not be automatically reported to the HSE and, if it is indeed a “true positive” result, close contacts will not be informed and could spread Covid-19 to others, the spokesperson added. 

There is also a risk with antigen tests that a person could receive a false positive or a false negative which could have implications for the person and others around them, they said. 

The official advice remains that if a person develops symptoms they should self-isolate and contact their GP who will arrange a free PCR test. 

However, rapid antigen testing is another weapon in our arsenal. 

The Government’s Expert Advisory Group on rapid testing last month recommended their widespread use in schools. Similarly, HIQA recently recommended the use of antigen testing in meat plants. 

(The HSE already carries out antigen testing twice per week in meat plants and has so far carried out over 20,000 of these tests, but it is also in addition to a monthly PCR test for employees.)

Professor of Experimental Immunology, School of Biochemistry and Immunology at Trinity College Dublin Kingston Mills, who sat on the Expert Advisory Group, said there are “huge benefits to antigen testing as an adjunct to PCR testing”. 

Mills told The Journal that people can be trusted to know how to self-administer a rapid antigen test but said people misinterpreting what a negative results means is “a worry”. 

“People could think ‘I’m not infectious, I don’t have Covid-19, I can do what I like’, that’s my biggest worry. I understand that concern,” said Mills, who said a public information campaign about the benefits and risk of these tests could help inform people. 

Speaking on RTÉ’s News At One yesterday, Dr Holohan said the issue was not a question of trusting the public but about “people’s interpretation of what the result means”. 

From NPHET’s perspective, it comes down to individual behaviour and informing people about the limitations of these antigen tests if they were to be used by the wider public who may purchase one in a supermarket. 

“The risk that we see is that if you get a negative test it might falsely reassure you… if it falsely reassures a person who is going to a wedding… now you’ve got the potential for a superspreading event to take place,” said Holohan. 

Tánaiste Leo Varadkar echoed this sentiment on Monday when he raised concerns about how LIDL had marketed their antigen testing kits, saying it sent out the “wrong message”. 

Varadkar said Government supports the wider use of antigen testing as Ireland reopens, and that guidelines to businesses carrying out rapid antigen testing would be issued shortly. But he said that the public should be aware of its limitations. 

With reporting by Nicky Ryan.