Analysis: Irish medical experts split down the middle over use of antigen testing

On Tuesday, Robert Read, director of the National Concert Hall, spoke to RTÉ’s Morning Ireland about the James Vincent McMorrow outdoor concert in Iveagh Gardens next week.

He was upbeat, understandably so, given that it will be the first of a series of pilots to test the safety of outdoor gatherings. Unsurprisingly, the 500 tickets sold out within minutes.

The audience would all take antigen tests before entering, he said. Indeed, the National Concert Hall has for months tested its own performers and staff before holding online concerts.

Two days previously, Tánaiste Leo Varadkar told RTÉ’s This Week that people would be tested and that he had “seen pilots like that run in other countries and I want them to be run here too”.

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Days before, Minister for Tourism, Culture, Arts, Gaeltacht, Sport and Media Catherine Martin said antigen testing was something that should be considered “but we’ll see what Nphet says”.

It quickly became clear on Tuesday what Nphet thought. Shortly after Morning Ireland, the NCH was told by Department of Culture officials that there would be no antigen testing.

What is more, it emerged there would be no antigen testing at any of the “pilot” events. None at all. Instead, they would rely on other social-distancing protocols.

It was a spectacular U-turn by the Department of Culture, followed by a milk and water statement that a “robust contact tracing system” would be in place, but this is more than collecting mobile phone numbers.

Speaking privately, a leading specialist sighed: “Why is Ireland different? Why is antigen testing being used without controversy in every other country except here?”

Dominant personalities

In short, dominant personalities in Nphet, chief medical officer Tony Holohan and Prof Philip Nolan, do not trust them. Nor does the HSE, which favours PCR tests.

The Irish debate has been unusually divisive. Earlier this year, the State’s chief scientific officer Prof Mark Ferguson examined the issue for the Government. The main recommendation of the report was that testing could play a role. There was a wrinkle, however. Two of the six members dissented, and they were, and are important players.

They were Dr Lorraine Doherty, the HSE’s national clinical director of health protection and Dr Darina O’Flanagan, ex- director of the health protection surveillance centre and special adviser to Nphet at the Department of Health.

Their reasons for dissenting were never set out. But as the weeks went by it became clear their reservations were shared by Nphet, the HSE and the Department of Health

“Snake oil”, Nphet’s head of modelling Prof Philip Nolan notoriously tweeted in May about Lidl antigen kits and the phrase for better or worse has stuck since.

On the other side, there are immunology scientists and infectious diseases specialists including Ferguson, Prof Paddy Mallon, Prof Mary Horgan, Prof Luke O’Neill, and Prof Kingston Mills.

One supporter is the Irish-trained Dr Susan Hopkins, who says: “Up to one in three who have coronavirus never show any symptoms, but that does not mean they are not infectious.”

“Antigen tests enable us to rapidly identify people who are asymptomatic, with results produced in 30 minutes,” says Hopkins, now the Covid-19 Strategic Response Director to Public Health England.

PCR tests are the gold standard, detecting the virus in infinitesimally small DNA fragments - but they are expensive, take 24 hours and need trained staff for the tests and the analysis.

Cheap as chips

Antigen testing which identify proteins on the surface of the virus are simple, cheap as chips, can be bought off the shelf as a DIY kit and give results in 20 minutes, just like pregnancy tests.

The downside is they are most accurate only when the person has a high viral load and is infectious. They are not so good at detecting Covid-19 early on or in the later stages of infection.

Ergo, the potential for false negatives. Critics, such as Prof Nolan, also think self-testing could lead to high error numbers and see people believing that they are not infected when they are.

By some reckonings, there are 2,500 different tests available, ranging from the highly accurate to the dangerously inaccurate. Just 12 of the 140 tested in the UK passed.

Acknowledging that they are not as accurate as PCRs, the majority Ferguson report said they could still offer “effective, meaningful” information in time to stop more infections.

Ultimately, the big debate about their use boils down to this: what happens when a person is given a false negative result. Will they behave as if they are not infected, and infect others?

Dr Holohan is particularly exercised about this: “A negative test will falsely reassure you. In every two cases in which an antigen test is done, it will miss it in one,” he said.

Supporters of antigen testing who contributed to this article acknowledge that they are not perfect: there will be self-testing errors, and they do not work optimally when overall case numbers are low.

Nevertheless, supporters such as Kingston Mills, professor of experimental immunology in TCD and a member of the Ferguson group, argue that they are better than no testing at all.

“That is the key to it. If you don’t do anything, you don’t find these people. Whereas if you do the testing you isolate, or get them tested first and then isolate them. That is the huge benefit of it.”

If used widely, people would be tested twice weekly. Those in the early stages of the virus who test negative would be “captured” by the next test, when they are infectious, say supporters.

The example used is Ireland’s meat plants. Last year, they saw large virus outbreaks, usually in busy and crowded boning halls where workers operate closely together in poorly ventilated rooms.

The rooms must be maintained at a constant 12 degrees and that means chilled air recirculation and no windows – all of which help to spread the virus.

Favours their use

The antigen tests that have taken place in such plants are led by Dr Donal Sammin, head of laboratories with the Department of Agriculture, who favours their use.

“Because they are not as sensitive as PCRs, they are actually only picking up those people that are shedding virus, the people you most want to exclude from the workplace,” he says.

Dr Sammin and his team began a pilot programme in 15 meat plants, doing 5,100 antigen testing in parallel to PCR testing. The PCR tests identified 79 positive cases.

By contrast, the antigen test identified only 43. It was less sensitive at picking up positive cases , but 41 of its positives were also picked up by PCR, so it was accurate when there was a high likelihood the person had Covid.

But what about the other side of the coin, what about the positives cases missed? When Dr Sammin’s team adjusted the PCR results to capture only infectious cases (and not all cases), the correlation was much closer, he says.

“[In one plant] we picked up 19 positive cases in a boning hall. All were confirmed on PCR, as were another 14. Most [of the 14] had already been asked to go home and isolate.”

Dr Eoghan de Barra is a consultant and senior lecturer in infectious diseases in the Royal College of Surgeons in Ireland, who checked manufacturers’s claims for antigen tests last year as part of his State research.

The tests performed really well where the person was symptomatic (90 per cent), but fell to 60 per cent accuracy, or below in asymptomatic cases. Nevertheless, De Barra sees their value.

“A large portion of people going to ‘asymptomatic’ walk-in centres are actually symptomatic but they don’t know they are. There are also many barriers to getting a PCR test.”

“How many people in their 20s will call their GP? What symptoms should you have before calling your GP?” he said, arguing that antigen testing could play a role for the young.

‘Human behaviour’

The key is human behaviour, he says. Will someone who gets a positive test go home, or will someone who “gets a negative result go out and throw caution to the wind.

“We succeeded because we changed human behaviour during the lockdown. We can fail because human behaviour being what it is will [lull] people into a false sense of security.”

Prof Nolan’s opposition, meanwhile, led to a rebuke by the pro-test Harvard epidemiologist Prof Michael Mina: “For an adviser to your Government – you don’t appear to know what you are talking about,” he said curtly..

Replying at length, Prof Nolan doubted that the tests are 100 per cent accurate for people transmitting virus and doubted, too, claims that the infections missed do not matter because those people are not transmitting.

Concerns that tests will miss a significant number of cases are not “confused” or “simply wrong”, he told his US critic: “We are not alone in the conclusions we have drawn.”

Some Ministers, however, are forging ahead. Minister for Higher Education Simon Harris has commissioned pilots in four universities, where rapid, repeated tests will be carried out on campus when students arrive back.