Manual contact-tracing is now bearing much of the burden of reaching those who may have been exposed to coronavirus

Credit: Hackney Council/Open Government Licence v3.0

The number of weekly contact-tracing alerts issued by the NHS Covid-19 app has fallen to fewer than 200,000.

Recently released data reveals that, in the seven-day period ending on 1 September, 195,967 app users across England received a notification that they had been in close contact with someone who tested positive for coronavirus shortly thereafter.

This figure is nearly level with the total number of positive results recorded during the same week: 191,967.

Earlier in the summer, the number of exposure notifications issued each week equated to nearly three alerts for every one positive case. The number of people reached via the app also far exceeded those contacted by manual contact tracers.

Now, the volume of notifications issued through the software each week is less than half the number of people being contacted directly by contact-tracing teams.

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In the week to 1 September, people that tested positive for coronavirus identified 415,168 others with whom they had been in close contact, and whose names and details were passed on to the Test and Trace programme; 350,622 of these were successfully reached by contact tracers and advised that they may need to isolate.

In total, the Test and Trace programme attempted to reach 611,135 people across England during the last week of August – equating to 3.2 for every positive test recorded – to notify them that had been exposed to coronavirus. Manual contact tracers did much of the heavy lifting, accounting for about seven in ten of these. 

This is a marked contrast with the early part of the summer; the first week of July saw a very similar number of new cases of the virus: 194,005.

But this led to more than 900,000 instances of close contacts being alerted – or 4.7 per for each positive test.

Almost 60% of those alerts came via the app, which issued 521,393 notifications that week. Some 380,948 contacts were passed on to manual contact tracers.

Steady decline
The number of weekly exposure alerts issued by the software peaked in the seven days to 21 July, when it reached 679,394. Since then, it has declined steadily each week, and is now at its lowest level since early June – a time when restrictions remained on all large gatherings, and visits to hospitality venues were still subject to the ‘rule of six’.

Across the whole of July, about 2.3 million alerts were sent by the Covid-19 app – each of which came with the instruction to self-isolate for 10 full days from the point of exposure. Many individuals and businesses were impacted by the so-called ‘pingdemic’, leading to fears that millions of users would choose to delete or disable the program.

The recent sharp drop-off in notifications – at a time when case numbers have remained steady – suggests that such fears may have been well-founded. 

The six most recent sets of Test and Trace data all recorded between 170,000 and 200,000 new weekly cases of coronavirus. During the same period, the volume of contact alerts sent by the app has fallen from nearly 700,000 to fewer than 200,000.

A small proportion of this decline can be attributed to a recent tweak to the app’s algorithm, which means that the exposure period for which contacts of asymptomatic coronavirus cases are notified has been reduced from five days to two.

But data also points to a major drop-off in usage of the technology, having shown that the use of the app to check in to venues for contact-tracing purposes has plummeted since restrictions were lifted on 19 July. In the last week of August, only 621,237 check-ins were made in English venues – 23 times less than the 14.5 million that were clocked during the final week of May.

Despite the lifting of restrictions – and the fact that fully vaccinated people are now instructed that they can take a test, rather than isolate, after being exposed to Covid – the government has continued to encourage people to use the contact-tracing app. 

But, even before the apparent major drop-off in usage in recent weeks, data showed that the near-28 million downloads recorded by the software could be more than 10 million higher than its number of active users.