Self-isolation alerts sent out by the NHS Covid app have plummeted by 43% in a week, government figures show.

A total of 395,971 alerts were sent in the week to 28 July telling people in England and Wales they had been in close contact with someone who had tested positive for coronavirus – down from 690,129 the week before.

Though reports have suggested that use of the app is decreasing, the large fall in alerts has been matched by a similar decline in the number of recorded cases over the same period.

A total of 189,232 people tested positive for Covid-19 in England at least once in the week to 28 July, down 39% on the previous week, according to the latest test and trace figures.

The number of check-ins to venues using the app also dropped. There were 2.4m check-ins in the week to 28 July in England and Wales – down 65% on the previous week.

A major incentive for having it downloaded was removed following the easing of coronavirus restrictions in England from 19 July onwards, when it ceased to be compulsory to check into venues, which most people did by scanning a QR code with the app.

The number of app downloads has shrunk dramatically since the rule change, while many others will have deleted it amid reports of a “pingdemic” of workers across the country being forced to isolate after receiving alerts, affecting supply chains and the economy.

People are “pinged” by the app if they check into a venue where someone tests positive. They are also alerted if their phone’s Bluetooth function detects a close continuous close contact with another app user who is later found to have coronavirus.

Karan Bilimoria, the CBI president, said the fall in alerts was welcome but said businesses were still struggling with self-isolating employees.

“It’s good to see a steep fall in those having to self-isolate, but this doesn’t mean the problem has gone away. The latest numbers remain too high and illustrate the frustration facing firms as existing staff shortages are exacerbated by unnecessary self-isolation. Amending the app is a welcome recognition of the problem but won’t provide the solution,” Lord Bilimoria said.

It was announced on Monday that the app was being updated so fewer contacts would be instructed to isolate after an increase in people being pinged since lockdown restrictions ended. That change has not been reflected in Thursday’s figures showing the drop in alerts.

The health secretary, Sajid Javid, said the “logic” behind the app was being tweaked, although the sensitivity and risk threshold would remain unchanged.

Instead of checking contacts for five days before a positive test, the app will only go back two days.

The rules for self-isolation will change significantly on 16 August, when people who have been fully vaccinated will no longer be required to isolate if contacted by NHS test and trace or the Covid-19 app, and will instead be advised to take a PCR test.