Rapid antigen tests open to manipulation, immunologist warns

Rapid antigen tests are open to manipulation and lack an evidence base to support their use, public health officials have warned.

National Public Health Emergency Team (Nphet) members doubled down on their criticisms of antigen testing during a sometimes stormy hearing of the Oireachtas transport committee on Wednesday.

Committee members called for wider use of antigen testing to help aviation recover from the 18-month Covid-19 pandemic, but Nphet officials said its role should be confined to supporting the “gold standard” PCR form of testing.

The use of rapid antigen tests to facilitate the reopening of society poses multiple risks due to their limitations and the lack of supporting evidence, chief medical officer Dr Tony Holohan warned.

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Dr Holohan urged “significant caution” about using antigen testing to “green light” or “enable” the resumption of activities after lockdown, “particularly while not accounting for the prevailing epidemiological situation”.

Antigen tests are cheap to perform and deliver results within minutes, but are less accurate than PCR tests.

Dr Holohan said Nphet was “more than willing to support the further use of the tests assuming evidence supports this and where real-world evaluation shows that can bring added benefit to the pandemic response”.

“Ultimately, however, based on knowledge to date, the safest way to reopen society, including to international travel, will be to continue to control disease incidence through a range of public health measures which are continuously reviewed, along with progressing the national vaccination programme to ensure as many people as possible within the population are protected through immunisation,” Dr Holohan told the committee.

The current epidemiological situation in Ireland remains stable and the outlook is broadly positive, he told the committee.

However, there is an “ongoing level of uncertainty” due to the threat of variants and while a significant proportion of the population have yet to be fully protected through vaccination.

Self-testing

Rapid antigen tests are open to manipulation when carried out by the person being tested, according to consultant immunologist Dr Mary Keogan. For this reason, self-testing is not used in any jurisdiction.

Dr Keogan showed the committee two tests she had manipulated, one with a buffer but no sample to get a negative result, the other with tonic water to get a false positive.

Internationally, the claims made by manufacturers of antigen tests about their sensitivity and specificity tended not to be borne out, she argued. Independent evaluations of the performance of the tests was needed.

Evaluating these tests is extremely labour intensive, she pointed out. For example, it took 80 nurses working 12-hour days to test 5,000 people who attended a pilot concert in Barcelona in March.

Four forms of PCR test have failed to meet the criteria for use in hospitals, Dr Keogan said.

Assistant chief medical officer Dr Ronan Glynn said there was a “misperception” that Nphet had not bothered to do studies on antigen testing when in reality they have not been done “here or elsewhere”.

There is not evidence to back their use internationally because other countries have not be able to do these studies to the required standard, he said.

Dr Holohan said there would be an extensive resumption of air travel in later summer, without the need for testing of passengers, provided virus levels were kept down and vaccination proceeds.

Asked why fully vaccinated people cannot fly now, he said the Government had made the decision to resume non-essential airline travel along with other EU states on July 19th. Before then, certification and other operational arrangements had to be put in place.

He pointed out that Ireland has had the fifth-lowest case numbers in Europe and the sixth-lowest death rate during the pandemic. “It’s not clear to me that if we had done something different without evidence, it would have changed things.”

Dr Holohan said he was open to a pilot evaluation of antigen testing in aviation. A pilot study is getting under way in third-level education, following a request by the Department of Education to the Department of Health. However, no similar request had been received from the Department of Transport in respect of the aviation sector, he told Labour’s Duncan Smith.

Croke Park

Nphet official Prof Philip Nolan gave the example of using antigen testing on 60,000 people attending a game in Croke Park. Typically, there might be 90 infections, including 40-50 people with symptoms who should not have been attending the event. The test would miss 20 infections and generate 120 false positives.

Prof Nolan questioned the use of a large amount of resources for such a small return.

Fianna Fáil’s James O’Connor criticised what he claimed was Ireland’s “lackadaisical” attitude to antigen testing and said it was “ludicrous” for the 140,000 people whose livelihood depended on aviation not to be looking at this form of testing.

Dr Holohan said the use of a test in a particular setting had first to be informed by well-run validation studies. “We can’t roll out tests on basis that people think they’re a good idea, without good quality validation studies.”

Breaking the chains of transmission cannot be achieved through testing alone, with the response also including case identification, contact tracing, clinical management of cases, infection control and disease surveillance, he said.

PCR testing, which can be carried out at a rate of 175,000 a week, remains the most accurate test for the virus, he said. Rapid antigen tests typically perform best in people with symptoms and in settings of high disease prevalence, and “less well” in asymptomatic people in low prevalence settings.

The HSE recommends the use of antigen tests as an adjunct or supplement to PCR and in vulnerable communities where follow-up of cases might be challenging, he pointed out. They are also being used in outbreak control, and their use has been evaluated in meat-processing plants.

Dr Holohan said there was still much to be learned about antigen tests and their actual, as opposed to hypothetical, benefits and limitations. The proper assessment of Covid-19 tests has been “neglected” up to now and many are brought to market “without appropriate real-world evaluation and well-designed studies” to evaluate them.

The current epidemiological situation in Ireland remains stable and the outlook is broadly positive, he told the committee.

However, there is an “ongoing level of uncertainty” due to the threat of variants and while a significant proportion of the population have yet to be fully protected through vaccination.