Q&A: How do I know the antigen testing kit I’m buying is reliable?

Ireland’s Covid-19 strategy will now include self-administered tests that give quick results

I read that the Government is introducing antigen tests to help prevent the further spread of Covid-19. How will this work?
Fully vaccinated close contacts of a confirmed Covid-19 case who are not showing symptoms of the disease will be sent a free antigen test in the post – the HSE has about two million in stock. If it detects Covid-19 they will be advised to have a follow-up PCR test, to confirm this result, and to self-isolate while awaiting that result. The HSE website will be updated this week to explain how to use the antigen test and report its result – a positive one will trigger an appointment for the PCR test. Close contacts of a Covid-19 case who aren't vaccinated and/or show symptoms of the disease should request a PCR test, as is currently required.

Are there other places where antigen tests will also now be used?
Yes, announcing the Government's new policy, on Tuesday, Taoiseach Micheál Martin also referred to the more widespread use of antigen tests for "certain events and activities", although he didn't specify whether these would be at entry points to large sporting events and concerts or in other places where large numbers of people gather indoors, such as conferences or trade fairs or in cinemas and theatres. The rapid-testing expert advisory group, chaired by Prof Mary Horgan, is expected to say next week where antigen testing will be recommended. "We have been working with researchers in Canada to see which settings there is evidence for the use of antigen testing. Antigen tests will be another layer of protection as we come into winter. They are not a substitute for other public-health measures, such as mask wearing," says Horgan, who is an infectious-disease consultant and president of the Royal College of Physicians in Ireland.

Aren't antigen tests already used in some healthcare and educational facilities and workplaces?
Yes, serial antigen testing is used with staff in some hospitals and nursing homes. It has also been used in meat-processing plants in Ireland since outbreaks in 2020. Five third-level institutions and 24 childcare facilities piloted the use of antigen testing with students and staff this year.

What are the benefits and risks of antigen tests compared with PCR tests?
The biggest advantage of antigen tests is their rapid results. An antigen test detects antigens – viral proteins – about 30 minutes after the saliva or nasal swab is taken, whereas the result of a PCR – or polymerase chain reaction – test can take at least a day to arrive from a laboratory. PCRs are the gold standard, as they can detect the genetic material of the Sars-CoV-2 virus before, while and after a person is infectious. Antigen tests are most likely to detect Covid-19 when the viral load is at its highest, which is when the person is most infectious, regardless of whether or not they have symptoms of Covid-19. Up to 30 per cent of people with Covid-19 have no symptoms yet can still transmit the virus. The biggest risk with antigen tests is a false positive or a false negative result. Antigen tests are also much cheaper, with self-administered kits costing less than €5 per test. (In the UK, the NHS will post seven lateral-flow antigen tests a day to whoever requests them; they can also be picked up free from pharmacies and other locations.) PCR tests, the swab for which must be taken by a healthcare professional and processed by a laboratory, are provided free in Ireland, with the cost met by the exchequer.


So isn't it about time that antigen tests were more widely used, given they are so much cheaper and faster than PCR tests?
Nphet, the National Public Health Emergency Team, advised against the widespread use of antigen tests in 2020, much to the frustration of some healthcare professionals and scientists, who saw them as a valuable extra tool in the fight against Covid-19. In June last year the chief medical officer, Dr Tony Holohan, warned people against buying antigen tests in supermarkets, saying they weren't reliable enough. The Department of Health later commissioned a report on antigen testing; it was published this spring. Prof Paddy Mallon, an infectious-disease consultant at St Vincent's University Hospital in Dublin, who was part of the advisory group that worked on the report, says, "Much of what is now being done at short notice with rising rates of Covid-19 could have been put in place a year ago. There has not been the same reluctance across Europe to embed antigen testing as a tool in the overall response to Covid-19." He regards antigen testing as mitigation measure that allows people to lead more normal lives. "Up to now there has been no system which reduces the risk of people participating in societal activities who transmit the virus without showing symptoms themselves."

If I want to use antigen tests on myself and my family before going to a wedding, a concert or a rugby or football match, how can I be assured I am buying a reliable testing kit?
The European Commission has compiled a list of scientifically validated Covid-19 rapid antigen tests, so consult its regularly updated PDF and look out for the CE mark before purchasing a test. On Thursday Holohan said it isn't a good idea for people with Covid-19 symptoms to use antigen tests and decide that a negative result gives them a green light to continue as normal. Booking a PCR test and restricting your movements while awaiting it are still what you need to do if you have symptoms.

Do you believe antigen tests are useful or snake oil? 

Sylvia Thompson

Sylvia Thompson

Sylvia Thompson, a contributor to The Irish Times, writes about health, heritage and the environment