Public health effectiveness of digital contact tracing in the COVID-19 pandemic: A systematic review of available data.

Background and aim Contact tracing is a key element of epidemiologic investigation and active surveillance during infectious diseases outbreaks. Digital contact tracing (DCT) are new technologies that have been increasingly adopted in different countries to support conventional contact tracing efforts to control the COVID-19 pandemic. However, scant evidence is available on its public health effectiveness. We applied the Indicator Framework issued in 2021 jointly by the World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC) to assess the available evidence on DCT adoption and impact in the context of the COVID-19 pandemic. Methods We carried out a systematic review following the PRISMA guidelines (Prospero registration number: CRD42021253662) to retrieve, pool, and critically appraise studies published in English from November 2019 to April 2021. We excluded mathematical models of effectiveness. Only studies representative of the general population or specific populations were included . In line with the WHO-ECDC indicator framework, outcomes of interest were grouped in indicators of: i) DCT use, ii) DCT success, and iii) DCT performance. Results We identified 1.201 citations searching the PubMed, Embase, Web of Science and The Cochrane Library. After screening, 10 studies were included. All included studies reported measures of DCT use, varying widely by study population and setting (percentage of DCT apps download from 0.01% to 58.3% in included studies). Almost no data quantified an association between DCT adoption rate and infection transmission at the community level. Only one reported measures of DCT success (ratio of exposure notifications received to positive test results entered), while no studies were retrieved reporting measures of DCT performance. Conclusions DCT has large potential to control epidemics. Its adoption is hindered by several normative, technical and acceptance barriers in different regions and countries. Our review shows that while some evidence is available on its adoption and use in selected settings, very scant data is available on its effectiveness in the fight against COVID-19. As digitalization provides new tools for infection control at the population level, solid research is needed to quantify the public health effects of their application.