Lateral flow tests could be failing -to detect thousands of Omicron cases every day, experts have warned.
Health chiefs have insisted the rapid kits, which give results in as little as 15 minutes, aren’t any less effective at spotting the variant.
But scientists argue the sheer volume of Omicron’s spread means huge numbers of infected Britons are being wrongly told they are negative.
The free tests are a key part of No10’s Plan B strategy, with vaccinated close contacts of positive cases told to use them daily for a week instead of isolating. Unvaccinated people must show proof of having a negative result to enter football stadiums.
Officials have also urged the public to use the kits before meeting loved ones in the run-up to Christmas, in a bid to quell the spread of Omicron.
But real-world evidence shows the tests, which can be ordered online or picked up at pharmacies, are just half as good as PCRs.
With Omicron showing no sign of slowing down as it spreads across Britain and up to a million lateral flows being carried out every day, it means tens of thousands of people may be receiving false negatives, scientists say.
Ministers fear the strain, which is already dominant in London, is infecting upwards of 200,000 people every day.
Dr Simon Clarke, a microbiologist at the University of Reading, said a negative result was ‘not proof’ that a person is not infected with the virus.
He warned even a one per cent false negative rate would thousands of people are being falsely diagnosed as virus-free, under the current swabbing levels seen across England.
Scores of Britons have complained about testing negative on lateral flows, only to be told they are positive by a PCR.
And one A&E doctor in London claimed he tested negative after using a lateral flow test that told him to only swab his nose. But when he used the same type of test to collect a throat sample, he was positive.
It comes as thousands of people have struggled to get hold of the tests this week, with the Government intermittently stopping orders from being placed. Chemists have even ran out of supplies on some days.
Experts told MailOnline the tests will ‘definitely miss’ positive cases and urged people not to test too often amid shortages. And top scientists warn lateral flow tests are just half as effective as PCR tests, which are processed in a lab and have a longer turnaround, and may pick up even fewer Omicron cases
LATERAL FLOW TESTING: 1million lateral flow tests were conducted in the UK yesterday, the highest level since January 6 (1.2million)
The Government website intermittently stopped orders for lateral flow tests from being placed, while thousands of pharmacies ran out. However, tests were available on Wednesday morning
WHAT HAS PREVIOUS RESEARCH SAID ABOUT COVID LATERAL FLOW TESTS’ ACCURACY?
Rapid coronavirus tests may miss four in 10 asymptomatic people, a major review concluded earlier on in the pandemic.
Researchers who analysed 64 studies of the effectiveness of lateral flow kits found they failed to detect 42 per cent of cases who didn’t show signs of illness.
The gold-standard Cochrane review found the tests, which give results in as little as 30 minutes, were better at catching symptomatic cases (78 per cent).
The findings have caused concern among some scientists because it’s thought that at least half of Covid transmission comes from patients who seem well.
Children are even less likely to fall ill with coronavirus but can still act as spreaders of the disease.
Hundreds of thousands of lateral flow tests are being used each day on teachers and pupils in a bid to keep schools open and Covid-free. They are also deployed in care homes, hospitals, and across businesses.
Professor Jon Deeks, a biostatistician at Birmingham University and co-author of the report, said ministers may have rushed lateral flow tests out in schools ‘without any supporting real-world evidence’.
The review also found lateral flow tests were prone to giving false positives, when a test says someone is infected but they aren’t.
Officials said there are plenty of tests and have entered new agreements with Royal Mail and Amazon to dish out more tests to homes and pharmacies.
Lateral flows are only supposed to be taken by people who do not have symptoms, while those without tell-tale signs of the virus are told to take a PCR, which is then analysed by laboratory technicians.
Preliminary evidence shows lateral flow tests are as effective at detecting Omicron as they were for Delta, according to the UKHSA. The agency is set to publish data on the efficacy rates tomorrow.
Fears were raised after one of the South African experts who raised the alarm about the super-variant warned lateral flow were less sensitive to Omicron.
Dr Angelique Coetzee, chair of the South African Medical Association, told MPs on the Science and Technology Committee: ‘The rapid test still showing false negatives in the early period.
‘We do have patients that waited a week and still have a headache and then they do PCR and it’s positive.’
But Dr Susan Hopkins, head of the UK Health Security Agency, told ministers the test will detect positive cases among those with and without symptoms.
She told MPs: ‘They’ve been used very effectively now for almost one year in the UK population.
‘What we know is that overall it will detect about 50 per cent of cases compared to PCR, but it will detect about 80 per cent or even more than that of people who have high amounts of virus and therefore are at the highest risk of transmitting to others.’
She added: ‘Again, the public health advices to take a lateral flow before you go out to socialise at the moment, we would recommend that.’
Dr Clarke told MailOnline a negative test is an indication someone is likely negative, but it’s ‘not proof’.
He said isolating close contacts of positive cases instead of daily lateral flow testing ‘is better’ but would leave too many people stuck at home.
The tests will reduce the number of infected people going out and spreading the virus, but ‘won’t eliminate them’, Dr Clarke said.
Twitter user Chris Stables said lateral flow tests indicated he was negative for three days after he tested positive on a PCR.
How to do a rapid lateral flow test
Rapid lateral flow tests are for people who do not have Covid symptoms, such as a high temperature, a cough or a loss or change to smell or taste.
The tests give a quick result using a device similar to a pregnancy test.
People with Covid symptoms should do a PCR test.
Before doing a rapid lateral flow test the NHS advises:
- try not to eat, drink, smoke or vape 30 minutes before doing the test as this may affect the result
- read the instructions carefully
- clean the surface you’re putting the test on
- check nothing in the test kit is damaged or broken
- start the test within 30 minutes of opening the test kit
If your test requires a throat swab:
- open your mouth wide and rub the swab over your tonsils (or where they would have been)
- avoid the end of the swab touching your teeth, tongue and gums
- put the same swab inside your nose (about 2.5 cm up or until you feel some resistance)
If your test requires a nose swab only:
- put the swab inside your nose (about 2.5 cm up)
Completing the test:
- put the end of the swab into the tube so it’s in the liquid
- squeeze the liquid from the tube onto the test strip
- check the waiting time in the instructions that came with your test kit
- wait for the time shown in your test kit instructions
- read your result
- report your result on the Government website
‘[The virus is] spreading through these false negative lateral tests when people think there negative when there not,’ he said.
British DJ Ruske tweeted that he had taken three lateral flow tests, two of which were negative, while one was positive.
And GP DR Helen Salisbury warned Omicron is ‘spreading like wildfire’ and people ‘may be infected even with negative lateral flow tests’.
Olympia Campbell tweeted that she had taken 10 of the tests in the last four days and all were negative, while a subsequent PCR indicated she was positive.
Meanwhile, Ryan Williams said on the social media platform that he tested positive on a PCR but negative on three lateral flow tests, warning ‘they aren’t the best at catching [the virus] early’.
Dr Alexander Edwards, an expert in biomedical technology at Reading University, told MailOnline it’s ‘hard to know’ how effective lateral flow tests are at slowing the spread of the virus.
He said: ‘They do work very well but are by no means perfect; their great advantage is speed and great convenience, compared to lab-based tests.
‘As long as people understand that they don’t always pick up every case, I think they can be very useful.
‘The exact accuracy has been measured in a range of settings, and doesn’t seem ideal — lateral flow tests definitely miss some PCR-positive people.
‘But as a trade-off, daily testing with a slightly less accurate test vs less regular testing with a far slower — yet more sensitive — PCR test may turn out to be more effective.’
He noted that alternative — vaccinated close contacts of Covid cases having to self-isolate — is inconvenient and can cause many who are unable to work from home to lose earnings.
Amid struggles posting the tests to people, Dr Edwards urged people to only ‘test when necessary’ rather than ‘as often as possible.
Professor Lawrence Young, a virologist oncologist at the University of Warwick, told MailOnline the tests are a ‘great tool’ for controlling the spread of Omicron, with some studies finding they pick up more than 90 per cent of the most infectious people.
He said: ‘The Flowflex kits that are being widely used are simple to use and rely on a nasal swab which is much easier than sampling the mouth and throat.
‘Of course there is a risk that infected individuals will be missed but we didn’t have this approach a year ago and having a test that is “real-time” without the inherent delays of PCR is extremely valuable.’
Professor Young added: ‘My mantra is “flow before you go” – we must encourage the responsible use of LFTs before people go out to mix with others.’