UK scientists question role of mass-testing on PM Johnson's road out of lockdown

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LONDON (Reuters) - The prevalence of COVID-19 cases in Britain might be so low that mass rapid lateral flow testing might do more harm than good, scientists said on Wednesday, as there could be more false positives generated than real cases detected.

Prime Minister Boris Johnson has made rapid testing a pillar of his plans to reopen England from coronavirus restrictions in June, along with the successful rollout of vaccines.

Infection rates have been falling, with 1 in 340 people in England estimated to have COVID-19 in the latest week.

Jon Deeks, Professor of Biostatistics at the University of Birmingham said that when prevalence drops, rapid tests would produce more false positives and less true positives.

"That's a mathematical certainty, and there's a point where you should stop (rapid tests). We may already be below that point," Deeks told reporters, adding that not enough thought was being put into when rapid tests would do more harm than good.

Deeks was speaking with other scientists presenting the results of a review of different rapid tests. He said there was less data on the accuracy of the Innova tests used in Britain, with other tests faring better.

Asked about the independent report, called the Cochrane Review, Public Health England said all the tests in use had undergone rigorous validation.

"As this report highlights, rapid tests are effective at detecting COVID-19 in people that are highly infectious, both with and without symptoms," Susan Hopkins, chief medical adviser to England's test and trace system said in a statement

"They are an absolutely crucial way to help bring down infection rates and keep them low."

Initial plans to test the entire population have not got off the ground, with the government instead seeing "targeted asymptomatic testing" as a way to break chains of transmission

Deeks said that rapid tests were less good at detecting asymptomatic people than those with symptoms, and doubted whether they could pick up people who were infectious.

(Reporting by Alistair Smout; editing by John Stonestreet)