Contact tracing: digital health on the frontline.

South Korea, China, and Singapore have successfully used digital contact tracing to control the spread of COVID-19, often putting public interest above individuals' right to privacy. Despite initial enthusiasm for this approach in the USA, Israel, and Europe, privacy concerns and technical issues inhibited uptake of digital contact tracing, and recent attempts to stem the first wave of SARS-COV-2 infections failed.

The Lancet Digital Health has published the first study reporting an assessment of the UK's Test and Trace contact tracing pilot programme on the Isle of Wight in May, 2020. Michelle Kendall and colleagues, who advised the UK Government on the design of the contact tracing programme, present modelling analyses that indicate significant decreases in COVID-19 incidence and R immediately after the launch of the Test and Trace programme. The Isle of Wight went from having one of the highest Rs in the UK (R=1·3) before the programme was launched on May 5, to one of the lowest (R=0·5) on June 14. The results indicate that Test and Trace interventions could have a positive impact in suppressing the UK COVID-19 epidemic. However, the study does not present causal evidence, and the data from cases traced by the contact tracing mobile app were not available, so the authors could not evaluate the effects of individual aspects of the Test and Trace programme.

In April, a Rapid Review published by the Ada Lovelace Institute reported that premature deployment of ineffective apps could undermine public trust and hamper the widespread uptake of tracking technologies. Uptake during the Test and Trace pilot programme on the Isle of Wight was only 38% and, in wider roll out of the programme, uptake could be as low as 10%.

In August, Braithwaite and colleagues published a Systematic Review, in which they highlighted that control of COVID-19 will require a high population uptake of contact tracing apps (56–95%). Similar to the network effect phenomenon, where increasing participants of a service directly increases the value to each user (eg, social networks), evidence of effectiveness directly affects uptake, while uptake directly affects effectiveness.

In May, Microsoft Research conducted a survey of over 4500 Americans to gauge the relationship between effectiveness and installing the app. Their results suggest that more than 60% of Americans would install an app that reduces their infection rate by 50%, and more than 75% of Americans would be willing to install an app that reduces their infection rate by 97%. Therefore, transparent analysis of the efficacy of contact tracing apps is needed to better engage the public and improve the effectiveness of contact tracing programmes.

In a modelling study published in The Lancet Infectious Diseases, Kucharski and colleagues concluded that contact tracing alone is not likely to contain the virus. They estimated that digital tracing alone reduced R by 44% and manual tracing of all contacts reduced R by 61%. Braithwaite and colleagues' Systematic Review did not find empirical evidence of the effectiveness of digital contact tracing without support from traditional contact tracing approaches, alongside measures such as remote working by a large proportion of the population and physical distancing.

Effectiveness and uptake of technology are not the only factors in determining the success of a contact tracing programme. Other factors include whether users self-isolate and get tested quickly. Reports predict that less than 20% of people in England fully self-isolate when asked to do so. We know that people without privilege and wealth have limited capacity to self-isolate at home, therefore it is vital that contact tracing strategies recognise the financial barriers to complying with public health measures. Furthermore, inadequate testing and delays in producing results have hindered efforts to contain major outbreaks in the UK and USA.

On Sept 26, SAGE warned the UK Government that the daily coronavirus death toll is set to more than double within 4 weeks. Given the scale and speed of the pandemic, digital contact tracing is imperative to curtail the second wave of COVID-19. Contact tracing must be adopted widely and integrated into public health strategies, including financial support to allow for quarantine and widespread rapid testing. The Lancet Digital Health calls for robust evaluation of global contact tracing approaches to stop the spread of SARS-COV-2 and future epidemics. The digital health community are on the frontline and, at this watershed moment, we must galvanise to end this pandemic.