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Rapid Covid tests No10 is using are too inaccurate, scientist warns
Rapid lateral flow Covid tests No10 is using as part of Operation Moonshot can do more harm than good because they are so inaccurate, scientist warns
- Tests are not sensitive enough when people use them themselves, experts say
- They fear people will get false sense of security from testing negative and go out
- Professor Deeks said Government not being clear about limitations of tests
Professor Jon Deeks, a biostatistician from the University of Birmingham, accused the Government of making lateral flow tests seem ‘better than they are’
Boris Johnson’s extortionate Operation Moonshot mass-swabbing scheme could accelerate Covid’s spread because the tests are so inaccurate, a top expert has warned.
Professor Jon Deeks, a testing expert at the University of Birmingham, accused the Government of making lateral flow tests seem ‘better than they are’ in a bid to justify the £100billion scheme.
Professor Deeks and other scientists are concerned that the tests are significantly less accurate when people do them themselves, as is the plan for Opertaion Mooonshot.
A trial of one test used by the Government found that it detected 79 per cent of coronavirus cases when administered by a trained professional but only 40 per cent in a real-world self-swabbing scenario. This is significantly lower than the more expensive but slower PCR tests which detect 70 to 99 per cent of positive cases.
Despite concerns about their reliability, the 15-minute tests – which the UK has spent more than £1billion on – are being offered to councils across England to be used as self-tests in schools, universities, care homes and in critical businesses to keep the country ticking over until everyone is vaccinated.
Over the weekend Business Secretary Alok Sharma suggested the rapid tests had the potential to make workplaces ‘completely safe’, while Matt Hancock claimed the quick tests had ‘been hugely successful in finding positive cases quickly’.
But Professor Deeks warned the tests missed 60 per cent of infected people in a mass trial in Liverpool when people swabbed themselves, a statistic which he feels is not being communicated to the public.
He told Sky News: ‘Government messaging on this hasn’t been explaining this to people and it’s a bit difficult. Most of us have never done a diagnostic test in our lives ourselves, and we would expect a positive to mean ‘yes’ and a negative to mean ‘no’.
Rouxel Maryline, a lorry driver travelling to Caen, France, via Portsmouth tonight at 11pm, receives a lateral flow test
There are currently four lateral flow test devices on the Government’s approved list.
SD Biosensor Standard Q Antigen Test
Manufacturer: SD Biosensor
When tested: August
Claimed accuracy: 95.5%
Real-world accuracy: Thought to be around 70% – source
SD Biosensor’s rapid coronavirus test
Innova Antigen Test
Manufacturer: Innova Medical
When tested: August
Claimed accuracy: 99%
Real-world accuracy: ‘At least 50 per cent’, according to Dept Health
Price: £8.69 per test (bulk order)
Innova’s rapid coronavirus test
Healgen Rapid Covid-19 Antigen Test
When tested: September
Claimed accuracy: 97.3%
Real-world accuracy: Unknown
Healgen’s rapid coronavirus test
SureScreen COVID-19 Coronavirus Rapid Antigen Test Cassette
When tested: December
Claimed accuracy: 98%
Real-world accuracy: Unknown
Surescreen’s Coronavirus Rapid Antibody Test Cassette
‘But here a positive means “probably” and a negative means “we really can’t tell”. So it’s a difficult message to get out to people, and I don’t think it’s been done at all well.’
Professor Deeks added: ‘This weekend the Business Minister was quoted as saying “This will make workplaces completely safe”. It’s not the right way to tell people about this.’
‘I think there’s an anxiety that, if we tell people the truth as to how bad this test is, people won’t bother getting it. But we have to do the truth – we can’t tell people that the test is better than it is.’
In a lateral flow test, a swab of the nose or throat is taken and then mixed with fluid that is applied to a piece of absorbent paper that will change colour to indicate whether or not the virus is present, taking just 15 to 30 minutes to produce a result.
Ministers have suggested the tests were a way to help regions come out of tougher lockdowns, enable relatives to visit care home residents and let schools open on time in January.
But there is fierce debate about whether they are effective enough to allow people to make decisions about their behaviour and movements.
University of Oxford researchers initially found the tests picked up 77 per cent of cases, rising to over 90 per cent of the most infectious.
However, accuracy fell from 79 per cent when used by experts to 58 per cent when carried out by ordinary people without any training. Real-world testing in Liverpool found the LFDs only picked up 41 per cent of cases when people were using them themselves.
The Scientific Advisory Group for Emergencies (Sage) said last month that lateral flow testing ‘should not be seen as a way on its own of enabling high-risk activities to take place, but could reduce the risk of activities that are due to occur anyway’.
Meanwhile, a blog published in The BMJ has called for the Government to rethink the rollout of the tests.
The article, published in the journal by Professor Deeks and colleagues, says extending the programme – which could potentially involve at home use – could cause ‘serious harm’.
‘We call on the Government urgently to change course,’ the authors write.
They add: ‘Low test accuracy would be less dangerous if people being tested and the public at large received accurate information about the risks and implications of a false negative result. Instead they are being misled.’
They conclude: ‘We call on the Government to at least to pause the rollout of rapid asymptomatic testing using the Innova test, including its use in care homes, schools, communities and self-testing by untrained people at home, until clearer messaging on the risks of negative results can be developed.’
The BMJ editorial came on the back of Professor Deeks’ own study into the reliability of lateral flow tests on students at the University of Birmingham.
Professor Deeks’ trial found that the test picked up on only two positive results out of 7,189 people.
To check how well the tests were working, experts at the university retested some of the students using a PCR machine, which is the test used by the Government and is up to 97 per cent accurate. PCR tests are analysed in laboratories and usually take at least a day to return a result.
Retesting around one in 10 of the students in the trial (710 out of 7,189), they found that six of them had wrongly been given negative results and were actually infected.
Multiplying this by 10 to take the whole group size into account suggested as many as 60 cases may have been missed.
HOW LATERAL FLOW TESTS ARE ONLY TRUSTWORTHY WHEN ADMINISTERED BY TRAINED STAFF
Lateral flow tests are only accurate at diagnosing coronavirus when administered by trained professionals, studies have repeatedly shown.
The tests, which give results in as little as 15 minutes, use swabs of the nose or throat. Samples are then mixed in a testing liquid and put into a plastic cassette which can detect the presence or absence of coronavirus and then produce an image of a line, the same way as a pregnancy test, to indicate whether it is positive or negative.
The Department of Health and NHS are instructing people to use the tests on themselves, despite manufacturers of some kits saying they shouldn’t be used as DIY swabs.
Both the swabbing procedure and the use of the test cassette can easily be done wrong and affect the accuracy of the test.
If the swab isn’t done for long enough, or deep enough into the nose or throat, it may not pick up fragments of virus. Medical professionals are also able to use nasopharyngeal swabs, which go right to the back of the nostril, whereas this is not advised for people who test themselves.
And if the sample isn’t properly inserted into the cassette the result might be wrong, or people may misread the display when it produces a result.
SELF-TESTING CUT ACCURACY FROM 79% TO 58%
A University of Oxford and Public Health England evaluation of the Innova lateral flow test, which is being widely used in the UK, found its sensitivity – the proportion of positive cases it detected – fell from 79 per cent to 58 per cent when it was used by untrained members of the public instead of lab experts.
Based on this evaluation, officials pushed ahead and used it for a real-world self-testing trial.
PILOT IN LIVERPOOL FOUND FEWER THAN HALF OF POSITIVES
When the same Innova test was trialled on members of the public in Liverpool – with people taking their own swabs and trained military staff operating the tests – the swabs picked up just 40 per cent of positive cases.
In the study the rapid tests detected 891 positive results, compared to lab-based PCR swabs that found 2,829 positives in the same group. This means 1,938 people got a wrong negative result from the rapid test.
The study didn’t compare this to professionally done rapid tests, but the manufacturer Innova claims its test is 95 per cent sensitive in lab conditions.
…BUT TESTING DONE BY MEDICS IN SLOVAKIA ‘REDUCED INFECTIONS’
Despite rapid lateral flow tests getting bad press, officials in Slovakia used them on 5.2million people – almost the entire population of 5.5m – in a trial that a study later estimated to have cut the country’s infection rate by 60 per cent.
The tests used were between 70 and 90 per cent accurate and all the swabs and evaluations were carried out by trained medical workers. They used deep nasopharyngeal swabs, that go to the back of the nose, whereas self-testing generally relies on a swab of only the nostril.
London School of Hygiene & Tropical Medicine researchers said that the scheme successfully weeded out coronavirus cases that wouldn’t have been found otherwise, slashing the number of cases by over half in a week during a lockdown.
HOW RAPID TESTS ARE DIFFERENT TO LAB-BASED PCR SWABS
Lateral flow tests are an alternative to the gold standard PCR test – known scientifically as polymerase chain reaction testing – which is more expensive and more labour-intensive but more accurate.
PCR tests also use a swab but this is then processed using high-tech laboratory equipment to analyse the genetic sequence of the sample to see if any of it matches the genes of coronavirus.
This is a much more long-winded and expensive process, involving multiple types of trained staff, and the analysis process can take hours, with the whole process from swab to someone receiving their result taking days.
It is significantly more accurate, however. In ideal conditions the tests are almost 100 per cent accurate at spotting the virus, although this may be more like 70 per cent in the real world.
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