The number of Covid-19 app alerts fell significantly in England and Wales in the last week of July, official statistics show.
Nearly 396,000 people were pinged, compared with the previous week’s record of 690,129, a fall of 43%.
The number of people reporting symptoms into the app also fell – 24,391 reports compared to 36,156 the week before.
Changes to the app, which will mean it notifies fewer close contacts, will be rolled out next week.
The number of positive tests linked to the app also fell 43% to just over 84,500 in England and Wales.
The latest numbers show two pings were issued by the NHS app in England for every reported case.
That is a fall from the previous week, but still well above levels seen in May when it was just over 1.1 isolation alerts for every reported case.
“Pings” are sent to people who have been using the app and have spent enough time close to another person with it, if that person later tests positive for Covid-19 and enters their result into the app.
Fewer contacts
The big fall in alerts sent by the app comes ahead of changes to the app intended to reduce the number of contacts advised to self-isolate following a close contact with a positive case.
From Monday the app will look for contacts two days prior, rather than five, when someone without symptoms tests positive.
Health Secretary Sajid Javid said it would reduce disruption, but still protect those at risk.
A number of industries, including car manufacturers, had complained that the number of staff isolating because of pings was disrupting production.
Some bar staff told the BBC managers had asked them to delete the app to avoid having to isolate.
The number of check-ins to venues using the app also saw a large decline.
In the week ending 28 July there were 2.4 million check-ins in England and Wales, down from 6.8m the week before – a drop of 65%.
The total number of downloads of the app also increased more slowly compared with the previous week.
However, the government is urging the public to continue using the app.
If you are “pinged” by the app you are advised – but not legally obliged – to self-isolate.
The government has allowed some key workers – such as those working in food distribution – to be exempt from having to self-isolate if pinged. Instead, they have to take daily tests.
A peer reviewed study published in May suggested that the app helped prevent several hundred thousand COVID-19 cases.