A meme has been established that smart phone contact tracing apps need at least 60% adoption to provide any benefit. That is not the correct interpretation as their could be detections at lower adoption levels, and if you detect anyone, then that is defined as a “benefit”, albeit, it may be a very small benefit – such as detecting one or two potential contacts, which is probably not sufficient to make any difference in disease spread.

MIT Technology Review cites Iceland as an example of 40% adoption rate and suggests this is a “significant level of adoption”.

Uhhh, no, and the source they cited to make this claim actually says the app “hasn’t helped much”.

Continue reading coronavirus apps do not need 60+% adoption to be effective  →

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.

Their Isle of Wight trial taught them several things – and the UK has now postponed the roll out of a smart phone contact tracing app until probably the end of the year.

Minister says smartphone tool was not a priority for the government at the moment

Source: NHS Covid-19 contact-tracing app for UK will not be ready before winter | World news | The Guardian

Update: The UK government terminated its contact tracing app trial, on going since the beginning of May and will now develop a new contact tracing app based on the Google/Apple Bluetooth tech.

More confusion and incoherent messaging in the public health domain:

A Covid-19 tracing software tool has appeared in the settings of both Android phones and iPhones as part of an update of their operating systems.

….

In the UK there is currently no available contact-tracing app.

The update has caused some confusion, with people querying the new addition to their handsets on social media.

Source: Coronavirus: New Covid-19 tracing tool appears on smartphones – BBC News

Sounds like the UK is starting over. Their original app used a central cloud-database and now they will develop an app based on the Bluetooth, no-cloud storage model.