The NHS Covid-19 app in England and Wales is being tweaked so fewer contacts will be advised to self-isolate following a close contact with a positive case.
The app will look for contacts two days prior, rather than five, when someone without symptoms tests positive.
Health Secretary Sajid Javid said it will reduce self-isolation disruption and protect those at risk.
The government is urging the public to continue using the app.
Scientists have estimated the app prevented up to 2,000 cases per day in the three weeks to 21 July when the number of self-isolation alerts – known as “pings” – rose by over 70,000 to a new record of 689,313.
And their analysis, which assumed 60% compliance with instructions to self-isolate, showed another 50,000 Covid cases were prevented by including chains of transmission.
This was estimated to have prevented 1,600 hospitalisations, the Department of Health and Social Care said.
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