Q&A: What you need to know about antigen testing in Ireland

What is happening with antigen tests?

The National Public Health Emergency Team (Nphet) has recommended that people engaging in what are described as high-risk activities, such as going to nightclubs and bars, should take at least two antigen tests a week.

Nphet had previously ruled out mass antigen testing because of the risk of people acting on false negatives.

However, an expert advisory group on rapid testing recommended that individuals who attend restaurants, cinemas, bars and nightclubs, or who participate in contact sports, multi-household visits or car-sharing, should use the tests regularly.

Department of Education officials are working with health authorities to introduce a programme of antigen testing of close contacts of confirmed cases in what were described as “specific primary school settings”.

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The Health Service Executive (HSE) is currently sending packs of five antigen tests to people deemed close contacts. If a person is deemed to be a close contact but is fully vaccinated and asymptomatic, they are asked to take an antigen test at home. If they are not fully vaccinated, they have to take a PCR test.

All household close contacts of a confirmed case should restrict their movements for five days, pending completion of three negative antigen test results within five days.

Where can I get reputable antigen tests?

There are no specific brands recommended but the European Commission has approved a long list of antigen tests that are deemed valid. Look for the CE mark on the box. The full list can be found here.

How do antigen tests work?

The antigen test looks for molecules on the surface of the virus. PCR tests look for genetic material from the virus. An antigen test is much faster than a PCR test, commonly giving results within 10 minutes.

The trade-off is that antigen tests are not as accurate as PCR tests. This is the main reason why Nphet has been reluctant to recommend them until now, but antigen tests have strong advocates, most notably Michael Mina, assistant epidemiology professor at Harvard University.

He told an Oireachtas committee last June that rapid tests were used to limit Covid's spread rather than to diagnose patients. Such tests are extremely accurate in detecting those who are infectious, as opposed to those who have small amounts of the virus, he said; therefore, antigen tests are a useful tool in stopping the spread of the virus.

He told the committee that data increasingly showed that using such rapid screening before large gatherings could cut the absolute risk of transmission after the event by 90-95 per cent.

How do you take an antigen test?

The test involves taking a swab in both nostrils, placing it in a solution and then waiting for the test result. The HSE has put an instruction video on YouTube. It can be accessed here.

How often do you have to take an antigen test?

Antigen testing is more accurate if you do a series of tests on different days. You can do them at any time of the day. In some cases, the test may not detect the presence of the virus. This is why the HSE recommends that household close contacts should take three tests over a period of five days.

What if I test positive for Covid-19 in an antigen test?

If a person tests positive using an antigen test, they should book a PCR test immediately. If a close contact develops symptoms while they are in the process of doing a series of antigen tests they need to self-isolate and book a PCR test.

Those whose antigen tests are negative are also asked to report their negative results via the HSE website. This is to monitor the accuracy of such tests.