Adoption of contact tracing app in France off to a very slow start

France was one of the first Western countries to build an app to track exposure to the coronavirus, but sluggish takeup rates could limit its usefulness in preventing a second wave.

Source: French Contact-Tracing App Struggles with Slow Adoption. It Isn’t Alone – WSJ

What many do not understand is that it requires a lot of people to have a smart phone and to install and use the app for a phone to detect potential coronavirus exposures.

To illustrate – in most modern countries about 80% of adults have a smart phone (plus or minus). When we adjust the figure for young kids who do not have a smart phone, about 2 in 3 people have a smart phone or 63%.

If half of all smart phone users install a contact tracing app, then we have about 32% have the app. In order to detect a contact, you need to be close to someone else with the same app. The probability of that occurring is .32 x .32 or 10%. Thus, what seems like wide spread adoption yields a potential of detecting just 10% of possible Covid-19 contacts.

And this probability does not take into account the problems with contact tracing apps:

  1. Incapable of detecting contacts across time (someone sits on a bus seat, coughs, gets up, leaves, and then you sit there)
  2. Difficulties with multi-path radio signals that result in false signal strength readings (this is common)
  3. Incapable of detecting when there is a barrier between contacts. For example, you are on a bus stopped at a bus stop while the driver takes a break. Someone with Covid-19 standing outside the bus results in alerting your phone that you just had a contact. Except you really did not due to the physical barrier.