Covid testing in schools is hugely disruptive and should be suspended, experts have said, as it emerged that up to 60 per cent of "positive" tests a week are coming back negative when checked.
Under plans to keep schools open, more than 50 million lateral flow tests have been carried out on youngsters, leading to thousands of pupils and their social bubbles being forced to self-isolate for 10 days.
But an analysis of NHS Test and Trace data by The Telegraph shows that, in secondary schools, one-third of lateral flow tests checked against the gold-standard Polymerase Chain Reaction (PCR) test have come back negative. In one week in March, that rose to 60 per cent.
In an interview with The Telegraph, Prof Sir Andrew Pollard, who led the Oxford vaccine programme, warned that mass testing was leading to such huge disruption in schools that it may be worth vaccinating youngsters to stop the chaos.
"If children are not severely affected, if they’re not major drivers of transmission, the testing itself is picking up lots of cases – causing classes to be sent home and so on – we’ve got to get to a point where we’re not impacting on education," he said. "And I think that impact on education could be a reason for vaccination.
"If children aren’t very much affected, then the testing is obviously not protecting them as they’re not very affected. So is the testing being done to protect other people?"
The Joint Committee on Vaccination and Immunisation (JCVI) is deciding whether to recommend jabs for children amid fears that the risks may outweigh the benefits.
Children and teenagers have been disproportionately impacted by measures to control the pandemic despite being largely unaffected by the virus.
Many have seen exams cancelled and been forced to homeschool for months, putting their mental health and socialisation at risk.
On Thursday, 23 British academics from universities including Oxford, Cambridge and University College London wrote to Gavin Williamson, the Education Secretary, to warn that lateral flow testing posed a danger for schools.
They are concerned that ongoing contact tracing trials could spark a wave of new infections and have called for them to be suspended.
Currently, 170 schools and colleges across England are taking part in the trials, in which students no longer need to self-isolate when a close contact tests positive if they test negative themselves using a lateral flow test.
But there have been concerns that as well as throwing up false positives, lateral flow devices miss large numbers of true positives. A pilot in Liverpool last year found they failed to spot positive cases around 50 per cent of the time.
The letter, published in the BMJ, reads: "It is undisputed that lateral flow tests (LFDs) cannot detect the lower levels of virus among individuals in early infection. There is a high chance that infected contacts in a classroom may be infectious before they are detected as positive by a LFD test."
The scientists said they were also concerned that the US Food and Drug Administration (FDA) had recently banned the Innova lateral flow test currently being used in schools, citing risk to health and "further spread of the virus". The FDA also said Innova had not provided evidence for efficacy of the tests.
On Thursday, the Medicines and Healthcare products Regulatory Agency (MHRA) said it had reassessed the Innova test following the FDA ban and had extended approval until August this year.
Graeme Tunbridge, the MHRA Director of Devices, said: "We have now concluded our review of the risk assessment and are satisfied that no further action is necessary or advisable at this time."
However, the Royal Statistical Society (RSS) warned that the regulator’s assessment of test safety needed to extend beyond physical safety to the consequences of false positives and false negatives for those tested, saying in a report: "The full range of consequences, from liberalised behaviour to deprivation of liberty, should be considered."
Analysis by The Telegraph shows that lateral flow tests are giving large numbers of false positives, leading to needless disruption in classrooms and beyond.
Around 19,000 infections were picked up by lateral flow devices in secondary school pupils between March and June – but despite new guidelines saying cases must be confirmed with a PCR test, only half were actually checked.
What's the difference between a PCR test and a lateral flow test?
Of the 9,546 checked, nearly one third came back negative – meaning almost 3,000 tests had to be removed from the daily reported figures. In June alone, more than 2,000 positive tests were quietly erased from the daily government dashboard, primarily because of problems with lateral flow testing.
The percentage of tests coming back negative in secondary schools reached 60 per cent in the week of March 4 to March 10, when 379 of the 624 positive tests were found to be wrong. It has since fallen to around one third.
If the negative rate holds true for the 9,500 unchecked tests, it suggests thousands more should be removed from the daily figures.
Experts warned that false positives not only caused disruption in schools but also made tracking the pandemic much harder.
Prof Carl Heneghan, the director of the Centre for Evidence Based Medicine at the University of Oxford, said: "What concerns me here is the idea that we are picking up such high numbers of false positives with lateral flow. And there seems to be a growing strategy of just using lateral flow for testing.
"It means we are getting a problem of inaccurate data. In evidence-based medicine we call this a problem of noise, and it’s difficult to see what is really going on amid this noise. At this point I would be ignoring lateral flow testing and be focusing on PCR positivity to get a true picture of the pandemic, and that shows cases are only going up in small incremental measures."
A spokesman for the Department for Education said daily contact testing as a replacement for self-isolation would be reviewed at the end of June. The Department of Health was contacted for comment.