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More than 1.7 million users of the NHS Covid-19 app in England and Wales have been advised to isolate following a contact testing positive, according to figures published by the Department of Health and Social Care (DHSC).

The app has been downloaded by 21.63 million users, representing 56% of those aged 16 of over who have a smartphone. The figures show  it is being used regularly by at least 16.5 million people, 49% of the eligible population.

Research carried out by the Turing Institute, which is currently undergoing peer review, suggests that the app helped prevent hundreds of thousands of infections between October and December last year. The authors of the paper used two different types of analysis, with modelling based on observed notifications suggesting 248,000 infections have been averted through the app, with 95% confidence that the actual number was within 60,000 of this.

The researchers also carried out a statistical comparison of local authorities with differing rates of usage, which suggested 594,000 infections had been avoided. However, this figure had a much wider 95% confidence range, of 317,000 to 914,000. DHSC mentioned only the second analysis in its announcement.

The app has been downloaded by 21.63 million users, representing 56% of those aged 16 of over who have a smartphone.

“The NHS Covid-19 app is an important tool in our pandemic response. We know it has instructed hundreds of thousands of at-risk people to self-isolate since it launched in September – including me – and this analysis shows it has been hugely effective at breaking chains of transmission, preventing an estimated 600,000 cases,” said health and social care secretary Matt Hancock.

The app was launched on 24 September, having been delayed by the abandoned development of a more privacy-invasive version. DHSC said it will start publishing weekly data on the app from Thursday 18 February, following a refusal last November of a Freedom of Information request from the BBC.

In an interim report on NHS Test and Trace published on 11 December, the National Audit Office said spending on the app by the end of October had reached £43m, exceeding a budget of £26m. It is working on a further report to be published this spring that among other things will examine the development and implementation of the app.