Digital Proximity Tracing in the COVID-19 Pandemic on Empirical Contact Networks

Abstract

Digital contact tracing is increasingly considered as a tool to control infectious disease outbreaks. As part of a broader test, trace, isolate, and quarantine strategy, digital contract tracing apps have been proposed to alleviate lock-downs, and to return societies to a more normal situation in the ongoing COVID-19 crisis. Early work evaluating digital contact tracing did not consider important features and heterogeneities present in real-world contact patterns which impact epidemic dynamics. Here, we fill this gap by considering a modeling framework informed by empirical high-resolution contact data to analyze the impact of digital contact tracing apps in the COVID-19 pandemic. We investigate how well contact tracing apps, coupled with the quarantine of identified contacts, can mitigate the spread of COVID-19 in realistic scenarios such as a university campus, a workplace, or a high school. We find that restrictive policies are more effective in confining the epidemics but come at the cost of quarantining a large part of the population. It is possible to avoid this effect by considering less strict policies, which only consider contacts with longer exposure and at shorter distance to be at risk. Our results also show that isolation and tracing can help keep re-emerging outbreaks under control provided that hygiene and social distancing measures limit the reproductive number to 1.5. Moreover, we confirm that a high level of app adoption is crucial to make digital contact tracing an effective measure. Our results may inform app-based contact tracing efforts currently being implemented across several countries worldwide.

Effectiveness of contact tracing apps for SARS-CoV-2: a rapid systematic review

“… 7–12 Included studies focused predominantly on the general population, although some analysed the effectiveness of CTAs for specific populations such as hospital personnel, or school children. 8 9 11 13–16 Especially in model-based studies, results were often presented graphically. Consequently, the effectiveness of CTAs on epidemiological and clinical outcomes was only partly, or not at all, reported in key numerical figures.…”

“…Table 2 provides an overview of characteristics and the most important input parameters used in models of the 15 included articles. Nine of the 15 model-based studies evaluated forward tracing CTAs, 8 9 11 13–18 four studies analysed bidirectional tracing CTAs 7 10 12 19 and one used an alternative method. 20 Four studies used a CTA that used sequential tracing.…”

“…Average incubation time, that is, the mean time between infection and symptom onset of SARS-CoV-2, was estimated to be 5–6 days for SARS-CoV-2. 9 11–21 The proportion of asymptomatic SARS-CoV-2 infections, used as input parameter in model-based studies, was estimated at 20%–50% based on empirical data, 8 9 16 18 but could vary between 18% and 86%. 9 The baseline R value chosen in the model-based studies varied between 1.2 and 4.0.…”

“…Nine of the 15 model-based studies assessed the effect of CTAs on reduction of R. 8 11 14–16 18 19 21 CTAs were able to control an ongoing outbreak or epidemic through quicker and more efficient feedback of a positive test result, and by notifying close contacts of a positively tested individual. 15 16 19 This speed and efficiency were not feasible using traditional manual contact tracing.…”

“… 16 New outbreaks could be controlled (ie, R c <1.0) by CTAs, by combining them with quarantine or self-isolation interventions, provided that hygiene and social distancing measures are maintained. 8 14 18 21 CTAs were able to reduce R by 0.3 more than traditional manual contact tracing, provided that feedback about contact with a positively tested individual is given to all contacts of the index case of the preceding 7 days. 19 Another model-based study demonstrated that a CTA with 20% adoption rate reduces R by 17.6% compared with no contact tracing, whereas traditional manual contact tracing reduced R by 2.5% compared with no contact tracing.…”