The effect of notification window length on the epidemiological impact of COVID-19 contact tracing mobile applications

Abstract

Background The reduction in SARS-CoV-2 transmission facilitated by mobile contact tracing applications (apps) depends both on the proportion of relevant contacts notified and on the probability that those contacts quarantine after notification. The proportion of relevant contacts notified depends upon the number of days preceding an infector’s positive test that their contacts are notified, which we refer to as an app’s notification window. Methods We use an epidemiological model of SARS-CoV-2 transmission that captures the profile of infection to consider the trade-off between notification window length and active app use. We focus on 5-day and 2-day windows, the notification windows of the NHS COVID-19 app in England and Wales before and after 2nd August 2021, respectively. Results Our analyses show that at the same level of active app use, 5-day windows result in larger reductions in transmission than 2-day windows. However, short notification windows can be more effective at reducing transmission if they are associated with higher levels of active app use and adherence to isolation upon notification. Conclusions Our results demonstrate the importance of understanding adherence to interventions when setting notification windows for COVID-19 contact tracing apps.

Individual level analysis of digital proximity tracing for COVID-19 in Belgium highlights major bottlenecks

“…The app’s technical sensitivity may benefit from more advanced proximity sensing technologies, such as ultra-wide band (UWB). Extending the contact elicitation window backward in time may help to identify source and sibling cases 50 , 51 . Finally, the integration of proximity sensing with an estimate of transmission risk in the immediate environment, e.g., through interaction with climate sensors, may further improve the transmission risk estimation algorithm 52 .…”

Modelling the effectiveness of isolation strategies for managing mpox outbreaks with variable infectiousness profiles

“…However, case identification may require a substantial public health investigation effort, and redundant isolation induces societal cost and burden for individuals 14,15 . Furthermore, more stringent control strategies may also lead to reduced efficacy due to non-adherence 16 . To mitigate these burdens, testing-based rules were applied during the COVID-19 pandemic 17,18 , which typically involved ending isolation following a specified number of successive negative PCR or antigen test results.…”