A scandal-hit Covid testing lab spotted 40 times less Covid cases in Sheffield than would be expected, it emerged today.
The facility, based in Woverhampton, reported that just 0.2 per cent of the Covid tests it analysed in Sheffield between September and mid-October were positive.
That is despite the broader test positivity rate in the city being around 8 per cent in that time.
Just four out of 2,400 Sheffield samples checked at the Immensa Health Clinic came back positive. Experts said they would have expected more than 200 positive results.
Earlier this month, health chiefs revealed 'technical issues' at the clinic, where workers have been filmed playing football and wrestling on shift, saw tens of thousands of tests wrongly processed over six weeks.
The UK Health Security Agency (UKHSA) said the false negatives were mostly sent to people who took a PCR test in the South West - where Covid cases are now nearly double the national average - but have refused to give specific breakdowns.
Experts said a full list of the testing sites affected by the testing problems should be published to assess the true scale of the error, amid fears it spurred on the latest wave of infections that saw daily cases hit more than 50,000 last week.
And leaders in Stroud in Gloucestershire, one of the areas worst affected by the testing problems, questioned how it took health chiefs so long to notice the lab problems and called for face masks to be brought in urgently to bring cases down.
The graph shows the proportion of people in Sheffield who took a PCR test (grey bars) and the proportion who tested positive (blue line). At the beginning of September, around 11 per cent of people were testing positive, but the figure fell to 7.4 per cent during the period when the Wolverhampton lab was experiencing 'technical issues'
Immensa Health Clinic, in Wolverhampton, has been suspended following an investigation revealing it may have incorrectly processed PCR tests. The lab (pictured) has been paid £170million by the taxpayer for its services
SHEFFIELD: Data shows that Sheffield sent 2,391 Covid samples to the Immensa lab between September 1 and when it was suspended earlier this month. But a local health chief said the problems had a limited impact locally, because the tests represent only a small proportion of the city's total. Some 410 per 100,000 people in Sheffield tested positive last week, lower than the national average of 482
Employees at Immensa Health Clinic in Wolverhampton were filmed fighting with each other (pictured) in January. This was at the height of the first wave and when the country was in strict lockdown
The UKHSA became aware of problems at the lab through an investigation it opened after hearing of people being sent PCR tests results stating they were Covid-negative after a lateral flow test indicated they were positive.
It found an issue with the Immensa lab — which had been given nearly £170million by the Government to analyse PCR swabs last spring — and suspended its Covid testing operations, sending swabs to other labs for examination instead.
UK's daily Covid cases are 'worryingly close to 100,000', symptom-tracking study claims
Britain is 'worryingly close' to recording 100,000 new Covid infections per day, the country's largest symptom-tracking study warned today despite Government data showing the outbreak is in retreat.
King's College London researchers estimated there were 92,953 people falling ill with the virus on average across the UK last week, up 14 per cent on the previous seven days.
Cases are rising across all age groups for the first time, with under-18s still making up the majority of cases after the back-to-school wave, with nearly 44,000 infected on any given day.
But there was also uptick in the rate of increase in 55 to 75-year-olds, the more vulnerable age groups, which increases the urgency for booster jabs, the researchers said.
Professor Tim Spector, the epidemiologist who leads the study, warned that the Government's figures were a 'big underestimate' and may be missing 40 per cent of cases.
It came as Sir Patrick Vallance today called on Boris Johnson to go 'hard and early' and reimpose Covid restrictions at the first sign of infections rebounding in the UK.
Ministers have insisted they will only move to Plan B if the NHS comes under 'unsustainable' pressure, with one senior source claiming that there was a 'less than 20 per cent' chance they will need to bring curbs back.
The latest survey figures from King's College were based on estimates from around 43,000 lateral flow and PCR tests done between October 9 and October 23. It relies on people coming forward to report their result, which experts say makes it susceptible to bias.
The Department of Health's daily reports only include cases confirmed by a PCR test — which are more reliable than lateral flow devices. They showed new infections fell for the fourth day in a row yesterday, dropping 10.6 per cent to 43,941.
Professor Spector's results cover the period when cases fell slightly in children, but not the most recent four days when infections fell across the country.
The agency estimates 43,000 people, mainly in the South West, were incorrectly told they were virus-free when they were infected and has contacted all those affected. It is still investigating what went wrong in the lab.
And now data from Sheffield in Yorkshire shows only four of the 2,391 tests it sent to the lab were found to be positive, while it reported 13 void results.
This equates to a 0.2 per cent positivity rate compared to the five to eight per cent national average at the time.
Around 20,000 people in Sheffield take a PCR test each day.
At the beginning of September, 11 per cent of people who took the test were Covid-positive.
But during the period when the lab thousands of tests were sent to was experiencing technical issues, the rate dipped to 7.4 per cent.
Dr Kit Yates, a mathematical biologist at the University of Bath, told the Guardian a list of every testing site affected by the Immensa problems should be published.
He said: 'It's all well and good notifying those people who were tested, but because of the nature of this communicable disease, this scandal now reaches well beyond those people
The public deserve to know if their area was affected and be reassured about the testing process, he said.
Dr Yates added: 'Beyond that it needs to be made clear that there are consequences for labs which don't do their jobs properly and whose mistakes results in higher-levels of infection, pressure on hospitals and ultimately in deaths.'
And Professor Paul Hunter, an epidemiologist at the University of East Anglia, told MailOnline he believed the 43,000 faulty test results impacted Covid case numbers.
He estimated 8,000 people will have caught the disease from a person given the wrong result, based on rough estimates about the number of people who isolate when they're unwell, regardless of PCR result.
But Professor Hunter said: 'It could be more, there are still several key unknowns here.'
'Clearly any substantial number of preventable false negatives means that people who would otherwise have been self-isolating are no longer doing so,' Professor Hunter said.
But Dr Eleanor Rutter, consultant in public health for Sheffield City Council said the problems at the Immensa lab'only affected a very small proportion of Sheffield's tests'.
She said: 'The number of people identified as potentially having been given a false negative result in Sheffield is incredibly small. There is nothing to suggest this has had a significant impact on infection rates in the city.
'Tests from the city are sent to many different labs across the country, and this particular lab only received a small percentage of them.'
The blunder does not seem to have greatly impacted infections in the city, where 410 people per 100,000 tested positive last week, compared to the national average of 482, Department of Health data shows.
But despite cases falling in the South West - in line with the pattern seen across the UK - infections are still nearly twice as high the region compared to the national average, with 728 per 100,000 people testing positive last week.
Dr Will Welfare, Incident Director for Covid at the UKHSA, said: 'We suspended testing at the Immensa Wolverhampton laboratory following an ongoing investigation into positive LFD results subsequently testing negative on PCR. Those affected were contacted as soon as possible.
SOUTH WEST: Official figures show figures are nearly double the national average in the South West, where 728 per 100,000 tested positive last week. The region has been the worst hit by the Covid testing problems at the Immensa lab in Wolverhampton
UK: Infections fell four a fourth day in a row yesterday. Latest estimates from the Department of Health show 482 per 100,000 people tested positive last week
'A full investigation remains ongoing and we will provide an update in due course.
'There is no evidence of any faults with LFD or PCR test kits themselves and the public should remain confident in using them and in other laboratory services currently provided.'
It comes as Labour, Lib Dem and Green leaders in Stroud, one of the areas worst affected by the testing problems, issued a joint statement calling for an urgent investigation into the lab and for mandatory face masks to be brought in to bring down infections.
Some 1,145 people per 100,000 people in Stroud tested positive last week, more than double than the average across the UK.
They leaders said: 'We've seen cases rising in our district like never before, and for weeks before Government announced that there was a lab testing failure, we were hearing local stories that something was not quite right with the tests.
'Why did it take so long for this failure to be detected and how many thousands of people has it affected? We can't afford for mistakes like this to happen during a pandemic.
'We call on Government to bring in urgent extra measures to get cases down quickly, such as mask wearing and extra ventilation in enclosed spaces and extra support for people needing to isolate.'
'People who have done all the right things are now ill with Covid and angry that the Government has denied any link between the test failures and increasingly high numbers of local cases.
'We are calling on our fellow Gloucestershire council leaders and our MPs to join us in demanding urgent action.'