Rapid Covid tests deployed to enable students to return home for Christmas, and care home residents to have visitors, are failing to identify up to 50 per cent of positive infections, according to the government’s own analysis.
Plans were this week rolled out across the UK for care homes to use the rapid tests to enable people to see their relatives and even briefly pause social distancing during visits, as students also began to head home at the opening of the travel window.
However, the failure of the devices to pick up enough cases has raised the risk of asymptomatic Covid carriers bringing the virus into care homes, or back to their family.
Experts have called into question the suitability and safety of the devices, which use lateral flow testing (LFT) to detect Covid-19 infections within a matter of minutes and are being implemented under the government’s Operation Moonshot plans.
Similar to a home pregnancy kit, these hand-held devices are currently being trialled among NHS staff, who are expected to test themselves twice a week to confirm their Covid status.
The tests are also being utilised under the government’s “test and release” strategy, enabling people to leave lockdown or to allow students to go home from university, and have been rolled out across Liverpool to conduct a mass testing programme there.
Downing Street has insisted that “extensive clinical evaluation” of the tests, conducted by Oxford University and Public Health England, has shown the devices to be “highly reliable, sensitive and accurate in multiple settings”.
However, experts have warned that the tests are “not fit for purpose” and called for an immediate halt to their use.
This comes after the government’s own analysis highlighted their lack of sensitivity in identifying positive cases.
A document released by the Department of Health and Social Care (DHSC) read: “In the field evaluation in Liverpool, compared to PCR tests, these tests picked up 5 out of 10 of the cases PCR detected and more than 7 out of 10 cases with higher viral loads, who are likely to be the most infectious.
“These tests will not pick up everyone who has Covid-19.”
This means about a third of the most potentially infectious people were not being told to self-isolate, therefore raising the risk of further transmission.
Previous laboratory validations had suggested the devices were susceptible to missing only 5 per cent of infections when a high level of virus was present in an individual.
This discrepancy is likely due to the fact laboratory tests are undertaken in a controlled environment where there is little scope for human error.
The DHSC also admits in its report that “some of the use envisaged by community testing may be outside the manufacturer’s instruction for use, for example self-swabbing and asymptomatic use”.
PCR tests – which require laboratory processing – are widely considered the gold standard, and are offered to people who have symptoms of Covid-19.
These tests miss fewer than 5 per cent of cases, according to government data.
The DHSC has yet to release a breakdown of its data on Liverpool’s mass testing programme, though the recent results suggest that for every 10 people who tested positive using the PCR method, only five will have been identified by the lateral flow tests.
“This test is not fit for purpose for the government's plans,” said Jon Deeks, a professor of biostatistics at the University of Birmingham and leader of the Cochrane Collaboration’s research into Covid-19 tests.
“It is totally unsafe to use these tests to decide somebody does not have Covid nor ‘infectious’. If it were a drug surely this would warrant an immediate withdrawal from use.
“Missing 30 per cent with high viral loads is not safe.”
In response to the government’s analysis, Sheffield City Council announced this week that rapid testing for care home visitors will be paused until further analysis of the devices has been completed.
Councils across Greater Manchester later followed suit over fears that results from the tests are inaccurate.
“We just want to know that LFT (lateral flow test) kits can be used safely to give accurate results in high-risk sensitive settings such as care homes and we’re seeking clarity on that from the DHSC,” said Greg Fell, director of public health in Sheffield.
“SAGE have not yet published evidence on this question, and we are waiting to see this before we take the next step.”
Prof Deeks said, “You cannot risk people with high viral loads visiting their elderly relatives.”
Dr Angela Raffle at the University of Bristol, who has worked on UK National Screening Programmes, said people with expertise in whole-population testing had not been consulted by the government for its mass testing plans.
“People who test negative may be falsely reassured and you could actually increase transmission,” she told the BBC.
Others have suggested that widespread community testing will still allow authorities to pick up cases that would have flown under the radar, helping to cut the chains of transmission and save lives.
“The accuracy of rapid antigen lateral flow tests is known to suffer somewhat from relatively low sensitivity compared to some RT-PCR methods,” said Alexander Edwards, an associate professor in Biomedical Technology at the University of Reading. “But there is a clear trade-off in speed, cost and convenience.”
Dr Susan Hopkins, senior medical adviser to Public Health England and NHS Test and Trace, described the tests as an “additional tool in helping us detect Covid-19 cases that we wouldn’t otherwise know about”.
A DHSC spokesperson said: “With up to a third of individuals with Covid-19 not displaying symptoms, broadening testing to identify those showing no symptoms and who can infect people unknowingly will mean finding positive cases more quickly and break chains of transmission.
“The country’s leading scientists have rigorously evaluated the Optigene LAMP test and Lateral Flow Test and confirmed the accuracy of the tests for asymptomatic testing.”