Figure 2. Overlap between standard CICT and digital notifications in a study of estimated cases averted by COVID-19 digital exposure notification, Pennsylvania, USA, November 8, 2020–January 2, 2021. During the study period, standard CICT resulted in interviews and contact elicitation from 20% of the reported cases (blue, shaded circle) and 3.2% of the population actively used the digital notification app (red, shaded circle). During case interviews, app users were provided validation codes for initiating contact notifications via their digital notification app (overlap of red and blue shaded circles; 0.2% of all cases). The effectiveness will be greater in the following scenarios. First, any case in the overlap of shaded red and unshaded blue circle (including persons who used at-home testing) can generate notifications via the app. Second, a larger shaded red circle reflects a higher proportion of the population actively using the digital notification app. Last, a larger unshaded black circle reflects a situation where more individuals can generate validation codes and receive exposure notifications. CICT, case investigation and contact tracing.