A systematic review of real-world contact tracing strategies at the onset of the COVID-19 pandemic

BACKGROUND: Contact tracing (CT) represented one of the core activities for the prevention and control of COVID-19 in the early phase of the pandemic, before the availability of effective vaccines. Poor evidence is available on the real-world implementation of CT strategies and adoption of CT digital tools during the initial phase of the emergency. METHODS: We aimed to provide a comprehensive picture of the organizational aspects of CT activities during the first wave of the pandemic, through the identification and description of CT strategies used in different settings during the period March-June 2020 and of digital tools adopted in the early phase. A systematic review of published studies describing organizational models of COVID-19 CT strategies and digital tools used in real-world settings was conducted. PubMed, Embase and Cochrane Library were searched. RESULTS: We retrieved a total of 1,637 studies, 30 of which met all our inclusion criteria. Seven studies target the general population, 10 studies described CT activities carried out in specific population subgroups, 13 described the use of CT apps in real world settings. Main activities implemented to rapidly scale-up CT activities included decentralization of CT, involvement of trained non-public health resources (e.g. University students, civil servants), use of digital tools for CT management, inter-agency collaboration, community engagement. Digital apps proved to be a useful supplementary component in CT strategies, however their acceptability was hampered by privacy, equity and effectiveness's concerns. CONCLUSIONS: Despite the lack of data on CT effectiveness, available evidence provides indication on coordination mechanisms and use of human and technical resources needed for the rapid scale up of CT activities. Further research on real world implementation of CT strategies during the COVID-19 pandemic would be needed to contribute to a more robust evidence-making process. KEY MESSAGES: • Decentralization of CT activities, involvement of trained non public health professionals, intersectoral collaboration were the key components of early COVID-19 CT strategies. • The use of smartphone apps and other digital tools proved to be a substantial support for CT activities. However, privacy, ethics and equity issues must be clearly addressed.