Mass coronavirus testing in Liverpool has missed half of positive cases, Government figures show, as scientists warned that plans for ‘moonshot’ testing could lead to many infected people believing they do not have the disease.
Community testing will soon be available for all local authorities in Tier 3 and the Government has suggested people could be allowed to visit pubs and meet friends if they test negative twice.
The mass testing programme, known as ‘Operation Moonshot’, uses lateral flow devices (LFDs). These are similar to pregnancy tests and give quick results, unlike usual polymerase chain reaction (PCR) tests which are sent to a laboratory.
However, results published by the Government this week from a pilot scheme in Liverpool show that compared to PCR tests, LFDs picked up just five out of 10 positive cases.
It means half of people who had coronavirus would wrongly believe they did not have the disease – and would be allowed to mingle in the community.
Jon Deeks, Professor of biostatistics at the University of Birmingham, called for an immediate halt to the ‘moonshot’ plan saying it put people at risk and was not fit for purpose.
“It is totally unsafe to use these tests to decide somebody does not have Covid nor ‘infectious’ he said, and sent a direct Tweet to the Health Secretary Matt Hancock and to Prime Minister Boris Johnson calling for lateral flow testing to be halted.
He added: “If it were a drug, surely this would warrant an immediate withdrawal from use.”
As well as problems with false negatives, the new Government guide also said it expected more than half of positive cases picked up under mass testing would be wrong, and advised people to get a separate PCR test to confirm they really did have the virus to avoid unnecessary isolation.
Although false positives do not risk greater transmission, they can mean large numbers of people – or entire classes –needing to self isolate, bringing widespread disruption to schools and businesses.
Explaining the problem, the document said: “The virus prevalence is around 1 per cent in the country, so we expect around seven true positives and four false positives for every 1,000 people tested.”
Commenting on the figures, experts said it was critical that people should be told that their test results may not be accurate.
Dr Alexander Edwards, associate professor in biomedical technology at Reading School of Pharmacy, University of Reading, said: “Participants must be fully informed that there is still a possibility they are infected even if they did not test positive, and be assured that a negative result does not make them ‘safe’."
“The positives of lower-accuracy mass testing: if you can pick up extra cases, and trace contacts, and isolate, you may be able to reduce transmission.
“The negative: false negatives might provide false reassurance, if this leads to increased spread the gains from identifying more real cases might be lost.”
Professor Rowland Kao, chair of veterinary epidemiology and data science at the University of Edinburgh, added: “It is absolutely correct to say that a negative on a lateral flow test should not be taken as a strong indicator of not being infected.
“Where the mass testing results are most valuable, is in providing a broad, relatively unbiased picture of how Covid-19 infection is distributed across a large population.
“This information could then be used to better assess the assignment of tier status for example, or where it might be valuable to place increased effort into contact tracing.”
On Thursday, NHS Test and Trace said contact tracers have now successfully reached more than one million people who have tested positive.
The percentage of contacts reached has also increased from 60.5 per cent to 72.5 per cent since last week, after contact tracers allowed parents to inform their children of the need to isolate.