By Bastian Rake
As transmissions from pre-symptomatic COVID-19 cases are common, manual contact tracing is ineffective to stop the spread of COVID-19. Infected individuals and those they were in contact with cannot be identified and isolated fast enough through manual contact tracing. On the other hand, contact tracing enables slowing down the spread of COVID-19 (or another infectious disease) by identifying those individuals who should self-isolate or be tested as they may have acquired the disease through having been in contact with an infected individual.
Mobile phone applications for contact tracing have been developed or are under development in many countries to avoid future social and economic lockdowns. To be effective and to be prepared for future waves of COVID-19 or other pandemics, these apps must be continuously used by a considerable share of the population. In particular, these can be very effective if they are adopted by at least 60% of the population or 80% of smartphone users. However, the much lower number of actual downloads in countries like Singapore and Iceland raise the question: How can the population be encouraged to use contact tracing apps?
For those who can use contact tracing apps ‐ because they have a smartphone that fulfills the technical requirements and have the competencies to use it – contact tracing apps must provide clear benefits that outweigh the cost of giving up control over sensitive information. When the spread of the disease is high or accelerating, there is an obvious individual health benefit as every user would be warned if they had close contact with someone infected by COVID-19, irrespective of where he or she met the person. However, this benefit depends on the number of users; contact tracing apps will generate very little benefit without a sufficient number of users. Therefore, it is important that the benefits of the apps are clearly and constantly communicated not only by governments, but also by medical doctors, academics, and prominent individuals – even each one of us as recommendations from friends and relatives are usually most effective. However, as explained before, the effectiveness of contact tracing apps requires adoption by a sizeable portion of the population. The effectiveness can decrease also when people get used to the message or perceive repetitions as annoying and, therefore, stop using contact tracing apps.
In addition, the benefits of contact tracing apps depend on whether and how the reporting of COVID-19 cases will work. Relying on self-reporting of symptoms or test results may decrease the perceived benefits of the app considerably as it is very likely that individuals either forget to report or underreport or overreport. In these cases, the perceived benefits are considerably reduced as the app would either not inform users or create false alerts. Both aspects are likely to lead to reducing the number of users as the perceived benefit for individuals becomes less obvious.
Even if the required number of users is initially met, the continuous widespread use of contact tracing apps will be the true challenge. Many digital services show a steep increase in the number of users right after being introduced, but their user base tends to erode rapidly shortly afterwards. Avoiding the decline in the number of users will not be easy and will require that users continuously see clear benefits.
If the strategies of keeping the spread of the virus under control are successful, the immediate individual benefit becomes less obvious. Instead, individuals may reassess whether the benefit offered by the apps exceeds the cost, such as giving up control over sensitive health-related data. The use of the apps may drop and society’s ability to react to a second wave of COVID-19 or a future pandemic will be reduced. Hence, contact tracing apps can only help to stop the pandemic if they are continuously used by many people. Otherwise, the virus may spread again and policy makers may have to decide on future lockdowns.