Why do some experts back rapid antigen tests for Covid while Dr Tony Holohan says they are only about 50pc accurate?
AND so the debate rumbles on. The divide between those who see Covid-19 antigen tests as hastening the road out of lockdown and others who regard them as too unreliable seems to be getting wider. Yesterday, Harvard professor Michael Mina said chief medical officer Dr Tony Holohan's views on the tests were wrong. Dr Holohan is cautious about their use, saying they are only 50pc accurate. In that case, someone who has the virus could wrongly believe they are in the clear. But the Harvard academic said their purpose is to detect people at their most infectious and limit spread. That way, antigen tests are good at preventing people from getting on flights or attending concerts. They are increasingly being employed in workplaces like construction sites, while a school in Limerick is providing them to students sitting Leaving Cert exams. The idea is to pick up someone who has the virus and stop them infecting colleagues. Health authorities here have been cool on the use of these tests. But there are many who advocate that, as the country opens up, more use of the wider number of tests available will help us accelerate out of lockdown. Polymerase chain reaction (PCR)  This is the standard test for Covid-19 used in HSE-run testing centres here. It is regarded as the gold standard. A PCR test involves taking a swab from up the persons nose or from the back of their throat. The swab is then sent to a laboratory where it is analysed. Read More  These are currently the most widely used tests, but can only determine if a person is infected with Covid-19 at the time. It does not show whether they have had it and have since recovered. It is then tested to see if the viruss genetic material, called RNA, is present. The person gets a result back in around 12 to 24 hours. Antigen testing  These are the kind of tests which can now be bought in some supermarkets here. Unlike PCR tests, which detect the viruss genetic material, antigen testing looks for proteins that are specific to the virus. They require a swab to be taken from the nose and are also only used to determine whether a person is currently infected. The process is usually quicker than PRC testing and can provide home results in as little as 15 minutes. It works like a pregnancy test, dipping the swab into a vial and putting drops onto a testing strip. The HSE says these tests are less reliable than PCR tests. They perform best where a person has a high viral load. The World Health Organisation currently says these tests should have more than 80pc sensitivity and more than 97pc specificity. The HSE uses these tests on hospital patients who have symptoms of Covid-19, including people attending an emergency department. Hospitals also use them in an outbreak of the virus. If someone gets a positive result in the workplace or at home, they should self-isolate. Prof Mina told the Oireachtas transport committee yesterday that these tests are sufficient to detect anyone who is likely to spread the virus. He pointed to data suggesting that using these tests before large gatherings could prevent 90pc to 95pc of transmissions. He added that testing someone in this way an hour before they board a flight is more likely to prevent transmission than getting a negative PCR result from several days before . Prof Mark Ferguson, the countrys chief scientific adviser, suggested that rapid antigen tests for arrivals into Ireland could potentially negate the need for mandatory hotel quarantine. The person would use them every day, uploading the result daily to a central database. He said the false-positive rate is one in 1,000 and there are also false negatives. Mixed views  An expert group set up by the Government reported in March and recommended widespread use of antigen tests. But they ended up split. The widespread use of the tests, including the potential for mass rollout in schools by September of this year, was not backed by all members of the group. A note at the end of the report said it was a majority report supported by four members of the six-person group, but not by two senior doctors in the Department of Health and the Health Service Executive. Loop-mediated isothermal amplification (LAMP) testing  Similar to PCR tests, LAMP testing also works by detecting whether the viruss RNA is present in a sample. However, the technology is able to produce results much quicker  in as little as two to three hours. While the tests also involve collecting nose and throat swabs, samples from mucus produced through coughing can also be used. Lateral flow tests  These portable tests can process samples on-site without the need for laboratory equipment, with most generating results in under half an hour. They are also able to detect coronavirus in people who do not show symptoms . While the swabbing and processing needs to be conducted by trained personnel, work is under way to see if the test could be self-administered. Antibody testing  These tests are used to tell if a person has previously been infected with coronavirus. Using a blood sample, the tests determine whether antibodies  which are produced by the immune system to fight the virus  are present. Pin-prick antibody tests, which allow people to submit their own sample, are not yet widely available but are be carried out at some private clinics here.