Britain’s failed covid-19 test results led to thousands of additional cases – Community News
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Britain’s failed covid-19 test results led to thousands of additional cases

ANMONG THE Tools that health officials have used to fight Covid-19, the effects of lockdowns, masks and vaccines have been well studied. Testing, the effect of which is difficult to measure because it coincides with other pandemic response policies, has received less attention. But thanks to a grim natural experiment, that’s now beginning to change.

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In September, covid appeared to come to a halt in southwestern Britain. Overnight stay, the positivity degree of PCR tests near Bath and Bristol fell from 3% to 1%. Nowhere else in England experienced a comparable decline.

Midway through the month, a local volunteer group said this apparent dip could be the result of faulty tests. A few weeks later, the group and local scientists asked the UK’s Health Security Agency (UKHSA) to investigate.

On October 12, the UKHSA to close a laboratory of Immensa, a testing company. The agency said the company falsely told 43,000 infected people they were virus-free. The cause of the error remains unclear. Immensa declined to comment.

Once the lab was closed, the reported number of Covid cases rose in the region. A spokesman for the prime minister said the lab errors did not cause this wave. However, on Nov. 14, Thiemo Fetzer of the University of Warwick released a paper showing that they probably did. It has not yet been peer-reviewed, but provides solid evidence that accurate testing does indeed slow the spread of Covid, by letting infectious people know to isolate.

To estimate what would have happened without the snafu, Mr Fetzer built a “synthetic control”: a group of areas whose past vaccination, testing and Covid cases and deaths matched those of the 13 most affected regions. The difference was big. From September 2 to October 12, the affected areas registered 13,000 fewer positive tests than the control. After that, they registered 21,000 more.

This means that each false test could have resulted in 0.6-1.6 extra cases (the spread reflects the uncertainty about how many people who tested positive previously received false negatives). Based on the UK death rate, this equates to 400-1,100 deaths.

Surprisingly, this toll is not the highest Mr Fetzer has attributed to technical problems. In 2020, a spreadsheet error prevented the UK’s statistics agency from reporting 15,000 covid cases to contact tracers. In a previous study, Mr. Fetzer that 1,500 people died as a result.

Sources: “Measuring the epidemiological impact of a false negative: evidence from a natural experiment”, by T. Fetzer, 2021; Bureau of National Statistics

This article appeared in the Graphics Details section of the print edition under the headline “An Immensa Cock-up”

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