A peer-reviewed study finds UK’s NHS contact-tracing app reduced the second wave by roughly 25%, averting ~594,000 out of 1.89M cases from October-December 2020 (BBC)

peerreviewed nhs 1.89m octoberdecember

The NHS contact-tracing app had a significant impact on lowering the spread of the coronavirus in the UK, a peer-reviewed paper has found.

Researchers estimate the app prevented hundreds of thousands of cases of the disease, and thousands of deaths.

“On average, each confirmed case who consented to notification of their contacts through the app prevented one new case,” the paper claims.

The research has been accepted for publication by the journal Nature.

Some of the researchers were themselves involved in the creation of the NHS contact-tracing app, and had previously released some of the estimates.

But the inclusion in Nature means the paper has now been peer-reviewed by other academics. It has been made available as a preview of papers due for publication.

Millions of notifications

The paper covers the time between the app’s launch on 24 September last year until the end of 2020. It was “used regularly” by 16.5 million people – about 28% of the UK population, the research says.

It works by using a smartphone’s sensors to measure how close a user is – and for how long – to other app users. If one of those people tests positive for coronavirus, the app can issue an alert telling those who have been in close contact to self-isolate.

It sent about 1.7 million “exposure notifications” after 560,000 app users tested positive, the research paper said.

They estimate that every 1% increase in app users resulted in cases being reduced by between 0.8% and 2.3%.

The difference between those two numbers comes down to two different ways the team used to calculate the impact of the app.

The first used a “modelling” approach, making assumptions about transmission and how strictly people stuck to quarantine. The second involved looking at data from local authorities on actual cases. Both were compared to how widely the app was used to estimate its impact.

Researchers said the number of cases prevented was 284,000 on the modelling approach, and 594,000 using the statistical one. That translated to 4,200 or 8,700 prevented deaths respectively.

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