COVID-19 Policy Primer: Digital Contact Tracing requires Speed, High Uptake and Demonstrated Value

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Digital contact tracing solutions for COVID-19 must offer exceptional speed and achieve high take-up rates to be useful, according to a working paper released by the Centre for Social Data Analytics (Auckland University of Technology) and the Institute for Social Science Research (The University of Queensland).

Australasian researchers led by Professor Rhema Vaithianathan (Auckland University of Technology, The University of Queensland) use a simple graphical model of infection transmissions to illustrate why COVID-19 is particularly challenging to manage with traditional manual contact tracing.

Speed

The researchers demonstrate how the epidemiological features of COVID-19 mean that, even before a patient becomes symptomatic, their contacts may have already infected a significant number of people.  Because so much of the transmission occurs before anyone even knows a person has COVID-19, once a positive test is generated and tracing starts, the process must be extremely fast. In fact if a person exposed to COVD-19 is contacted more than a week after the infected person first showed symptoms, there is little value in isolating the exposed person, because (on average) they would have already finished passing on COVID-19 to others.

“With COVID-19 it is the speed with which people who might have been exposed are found and isolated that is important, rather than how comprehensively all those people are identified,” says Professor Vaithianathan.

“Enhanced manual tracing apps like Australia’s COVIDSafe are designed to supply manual contact tracers with the details of exposed people who may otherwise be missed, but because those apps don’t support automated notifications, they just can’t inject enough speed to improve transmission control.”

The researchers come down firmly on the side of contact tracing solutions that offer instantaneous notifications (with the opportunity for follow up by public health officers to ensure isolation has occurred).

“Since speed is the most crucial element for controlling the spread of COVID-19, it is unlikely that enhanced manual tracing solutions such as COVIDSafe can do much to reduce reproduction rates,” says Vaithianathan.

Uptake

Assuming that an instantaneous solution is adopted, the researchers explain how policymakers can identify the minimum take-up rate for the solution to be useful.

The researchers find that uptake of digital solutions only starts adding significant value (by taking work off manual contact tracers) at take-up levels above 60 per cent, suggesting that targets like 40 per cent (adopted by Australia) are simply too low.

Demonstrating Value

Given the need for high uptake, the researchers find that building and maintaining social licence for the use of digital tools is critical.  Governments need to demonstrate that the value to the user is high and that privacy and security risks are low.

Because users have limited ability to judge the value of contact tracing tools, high trust is needed to achieve high take-up levels.

The authors suggest that governments committing to an impact evaluation that will allow citizens to judge the impact of a tool will increase trust as well as take-up.

“We hope this working paper offers useful information and guidance for policymakers who are required to make high stakes decisions about digital contact tracing options both in the context of COVID-19 and beyond,” says Professor Vaithianathan.

Source: Centre for Social Data Analytics media release, 4 June 2020

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