Effectiveness of a COVID-19 contact tracing app in a simulation model with indirect and informal contact tracing

Abstract

AbstractDuring the COVID-19 pandemic, contact tracing was used to identify individuals who had been in contact with a confirmed case so that these contacted individuals could be tested and quarantined to prevent further spread of the SARS-CoV-2 virus. Many countries developed mobile apps to find these contacted individuals faster. We evaluate the epidemiological effectiveness of the Dutch app CoronaMelder, where we measure effectiveness as the reduction of the reproduction number R. To this end, we use a simulation model of SARS-CoV-2 spread and contact tracing, informed by data collected during the study period (December 2020 - March 2021) in the Netherlands. We show that the tracing app caused a clear but small reduction of the reproduction number, and the magnitude of the effect was found to be robust in sensitivity analyses. The app could have been more effective if more people had used it, and if time intervals between symptom onset and reporting of contacts would have been shorter. The model used is novel as it accounts for the clustered nature of social networks and as it accounts for cases informally alerting their contacts directly after symptom onset, without involvement of health authorities or a tracing app.