At least seven million people will need to download the new NHS Test and Trace Covid app for it to start reducing the spread of the virus, according to government estimates.
The new smartphone app was finally launched on Thursday, after months of setbacks, to allow users to find out quickly if they have been within close proximity of anyone with coronavirus and whether they need to get a test.
It will also allow the public in England and Wales to scan for QR codes in specific locations such as pubs and restaurants, to make it easier if they need to be traced following any outbreaks.
Developers of the app are working on the assumptions in Oxford University research which suggests that a minimum of 15% take-up is needed in a population in order to have any “meaningful impact” on the reproduction or ‘R’ number of the virus.
With 49 million people over the age of 16 eligible to use the app in England and Wales, that means roughly seven million users will be required in order to affect the spread of the disease.
The ‘R’ has risen above 1 in recent weeks, meaning the virus is now spreading rather than shrinking. Latest estimates are that cases are doubling every seven days.
Other similar apps in Germany and elsewhere have seen take-up rates of between 10% and 30% and the UK’s pilot schemes in Newham and the Isle Of Wight have seen results within that range.
However, earlier this year an Oxford University team had estimated that 56% of the general population must use an app to halt the outbreak - equivalent to 80% of all existing smartphone owners.
One problem for the contact tracing feature of the app is that its Bluetooth technology is estimated to produce “false positives” for a third of people told to self-isolate.
That’s why its status has been downgraded from “crucial” to stopping Covid’s spread to now just “the cherry on the cake”.
Its usefulness may come more from making it easier to check in to pubs and restaurants, get advice on social...