The debate around what role rapid Covid-19 testing should have on the speed at which society opens up moved up a gear on Wednesday.

Hundreds of workers from the aviation sector took their message to the offices of the Chief Medical Officer, calling for rapid antigen testing for passengers to be rolled out.

Other sectors, as well as some public health experts, have been advocating for greater use of antigen testing.

NPHET has said it would support increased antigen testing if studies show the benefit.

But how does antigen testing differ from PCR testing, which up until now we are likely more familiar with in Ireland?

Testing

For rapid antigen testing, the tester will use a swab to take a sample from a person's nose. This may be uncomfortable but it should not be painful. The sample can then be quickly tested on-site.

With a PCR test, a sample is taken from inside the back of the throat and nose using a swab. Like with an antigen test, this process can be somewhat uncomfortable. The sample then needs to be sent to a laboratory to be tested.

Speed

The result of an antigen test is generally available in less than an hour, and it can be as quick as 15 minutes.

However, getting the result of a PCR test takes significantly longer. At its quickest, a result could be available within a few hours but it is far more likely to take a number of days, or even up to a week.

Accuracy

While antigen testing can be much quicker than PCR testing, it is less accurate.

As the HSE points out though, no test is 100% accurate and all tests have limitations.

A PCR test is able to detect a COVID-19 infection even before the person becomes infectious. PCR testing can detect very small amounts of virus levels.

A rapid antigen test, on the other hand, reveals patients at the peak of the infection when the body has the highest concentration of viral proteins. The test will find the virus in most people who have symptoms but, in some cases, it may not pick up the virus at all.

In addition, PCR tests have a lower chance of false-negative results, while a drawback of antigen testing is that it has a higher rate of false-negatives.

Cost

Antigen testing is considerably cheaper than PCR testing.

The cost of getting an antigen test done through a medical provider in Ireland can cost anywhere from around €40 to €80. While cheaper home antigen testing kits are also becoming more widely available to buy, with some costing as little as €5 per test.

Due to the more complex process involved, PCR tests are more expensive with the cheapest ones costing around €90. However, they usually cost in the region of €120 to €150.

Where can antigen testing be most appropriately used?

Public health experts who advocate for more rapid antigen testing to be used are generally keen to stress that they should not be considered as a replacement for a PCR test, but could be used in public life to improve Covid-19 detection rates.

For example, internationally airports, arenas, theme parks, and other crowded areas provide rapid antigen testing to screen for potential positive cases.

Rapid tests will not catch every Covid-19 case, but they can catch at least some cases that would have otherwise gone unnoticed.

And their use is growing in certain countries. For example, in parts of Germany anyone looking to eat in a restaurant or exercise in a gym needs to provide a negative antigen test result that is no older than 48 hours.

Here in Ireland, antigen testing has so far mostly been used for people travelling, as well as for certain industries such as in meat factories where significant clusters of Covid-19 cases had been detected.