Engagement and adherence trade-offs for SARS-CoV-2 contact tracing

Abstract

Contact tracing is an important tool for allowing countries to ease lockdown policies introduced to combat SARS-CoV-2. For contact tracing to be effective, those with symptoms must self-report themselves while their contacts must self-isolate when asked. However, policies such as legal enforcement of self-isolation can create trade-offs by dissuading individuals from self-reporting. We use an existing branching process model to examine which aspects of contact tracing adherence should be prioritised. We consider an inverse relationship between self-isolation adherence and self-reporting engagement, assuming that increasingly strict self-isolation policies will result in fewer individuals self-reporting to the programme. We find that policies that increase the verage duration of self-isolation, or that increase the probability that people self-isolate at all, at the expense of reduced self-reporting rate, will not decrease the risk of a large outbreak and may increase the risk, depending on the strength of the trade-off. These results suggest that policies to increase self-isolation adherence should be implemented carefully. Policies that increase self-isolation adherence at the cost of self-reporting rates should be avoided.

Using a household-structured branching process to analyse contact tracing in the SARS-CoV-2 pandemic

“…The publication in this issue includes analyses up until August 2020. Since then, the model has been used to investigate and report via SPI-M/SAGE a range of other TTI policy choices including: out-of-household isolation of cases or quarantine of vulnerable household members; trade-offs between lengths of quarantine and uptake/adherence to symptomatic testing and quarantine, in recognition of challenges in uptake and adherence to policies as implemented (along with another contact tracing model described here [ 63 ]); and the implications for TTI effectiveness of limited testing capacity, an analysis that clarified the need to maintain testing capacity where prevalence is still low to avoid local epidemics spiralling out of hand precisely where contact tracing is more likely to succeed at achieving control. More recent work involves investigations into daily contact testing using lateral flow tests in lieu of quarantine [ 64 ], testing and quarantining strategies of travellers returning to households from abroad [ 65 ], and potential changes to the symptom criteria required for PCR-testing.…”

Will an outbreak exceed available resources for control? Estimating the risk from invading pathogens using practical definitions of a severe epidemic

“…In that study, resurgence was said to have occurred when the number of individuals who are symptomatic infectious reached 100. Other studies have also defined ‘large outbreaks’ as those in which a threshold number of cases is exceeded [ 88 , 89 ]. However, while threshold values were reported clearly in all these studies, we emphasize that the precise type of threshold and the value used should be chosen according to practical relevance in the particular scenario under consideration.…”

Fostering Participation in Digital Public Health Interventions: The Case of Digital Contact Tracing

“…Concerning regulations in general, it also needs to be taken into account that regulation which is only indirectly connected to the respective public health intervention might exert spillovers on people's participation and compliance. This is pointed out by Lucas et al (2020), who argue that stricter legal enforcement of selfisolation measures for people infected with SARS-CoV-2 could be associated with a decreasing willingness to report an infection and to comply with contact tracing measures. This could be explained by stricter regulations increasing the individual costs of compliance.…”

“…The same applies to the establishment of an oversight board to ensure the compliance with the regulatory framework (Amit et al, 2020). Governments fostering the adoption of digital contact tracing also need to consider the potential adverse effects that other public health regulations, such as quarantine measures, can have on the willingness to adopt and use digital contact tracing (Lucas et al, 2020).…”