Mobile phone apps are slowing down the pandemic

In the fight against the COVID-19 pandemic, contact tracing, that is, the system that warns people if they have been in contact with people infected with SARS-CoV-2, is a key element in helping to limit the spread of the virus. Smartphone apps allow automatic, digital, contact tracing, notifying someone if he/she has been in contact with a confirmed case of COVID-19 and issuing instructions for self-isolating. In a study carried out by British researchers at the University of Oxford (Zühlke Engineering Ltd, Alan Turing Institute), the effectiveness of these mobile apps, which have not been long in use and whose epidemiological impact is still to be determined, was analysed.

The researchers concentrated on the contact tracing app put in operation in England and Wales from the 24^th September 2020. By the end of December 2020, the app had been downloaded 21 million times (out of a total of 33,7 million eligible smartphones) and 16,5 million people (28% of the population) were using it regularly. In total, there were 1,7 million notifications to the contacts of confirmed cases, with an average of 4,4 notifications per infected person. According to modelling, for 1% more users, the number of infections could be reduced by between 0,8 and 2,3%.

It was estimated that 6% of individuals notified as contacts by the application were infected (with symptoms or a positive test result). This rate is comparable to contact tracing carried out by hand, without recourse to a mobile app. In this latter case, individuals who fell ill are questioned and their contacts informed orally or by SMS. But the mobile app does allow contact to be made more quickly. The 2 approaches are therefore complementary, but apps cannot totally replace other methods.