ABSTRACT
The COVID-19 pandemic has spurred an unprecedented demand for interventions that can reduce disease spread without excessively restricting daily activity, given negative impacts on mental health and economic outcomes. Digital contact tracing (DCT) apps have emerged as a component of the epidemic management toolkit. Existing DCT apps typically recommend quarantine to all digitally-recorded contacts of test-confirmed cases. Over-reliance on testing may, however, impede the effectiveness of such apps, since by the time cases are confirmed through testing, onward transmissions are likely to have occurred. Furthermore, most cases are infectious over a short period; only a subset of their contacts are likely to become infected. These apps do not fully utilize data sources to base their predictions of transmission risk during an encounter, leading to recommendations of quarantine to many uninfected people and associated slowdowns in economic activity. This phenomenon, commonly termed as "pingdemic," may additionally contribute to reduced compliance to public health measures. In this work, we propose a novel DCT framework, Proactive Contact Tracing (PCT), which uses multiple sources of information (e.g. self-reported symptoms, received messages from contacts) to estimate app users' infectiousness histories and provide behavioral recommendations. PCT methods are by design proactive, predicting spread before it occurs. We present an interpretable instance of this framework, the Rule-based PCT algorithm, designed via a multi-disciplinary collaboration among epidemiologists, computer scientists, and behavior experts. Finally, we develop an agent-based model that allows us to compare different DCT methods and evaluate their performance in negotiating the trade-off between epidemic control and restricting population mobility. Performing extensive sensitivity analysis across user behavior, public health policy, and virological parameters, we compare Rule-based PCT to i) binary contact tracing (BCT), which exclusively relies on test results and recommends a fixed-duration quarantine, and ii) household quarantine (HQ). Our results suggest that both BCT and Rule-based PCT improve upon HQ, however, Rule-based PCT is more efficient at controlling spread of disease than BCT across a range of scenarios. In terms of cost-effectiveness, we show that Rule-based PCT pareto-dominates BCT, as demonstrated by a decrease in Disability Adjusted Life Years, as well as Temporary Productivity Loss. Overall, we find that Rule-based PCT outperforms existing approaches across a varying range of parameters. By leveraging anonymized infectiousness estimates received from digitally-recorded contacts, PCT is able to notify potentially infected users earlier than BCT methods and prevent onward transmissions. Our results suggest that PCT-based applications could be a useful tool in managing future epidemics.
ABSTRACT
The BCG vaccine is a widely given vaccine against tuberculosis (TB), yet studies on effectiveness have shown considerable heterogeneity; as a result, BCG vaccine policies vary greatly across the globe and change across geography, and with time and disease burden. The recently updated third BCG World Atlas (www.bcgatlas.org) is a publicly available online database with information on BCG practices across 194 countries. This helpful resource has been used for over 10 years to support clinicians, TB researchers and TB vaccine development worldwide. Here, we summarise main findings from the third BCG Atlas' most recent update which included additional data collected around BCG strain type, vaccine stockouts and associated changes. Longitudinal analysis enables evaluation of changes in TB incidence over time, a method becoming more common in legislation interventions. A large number of countries in the BCG Atlas (156/194 countries) maintain universal neonatal BCG vaccination, of which 51 are considered low TB burden countries. We demonstrate the majority of countries who changed their national policy moved to targeted vaccination for high-risk groups, were in Europe and also had significant decreases in TB incidence both before and after policy change. Globally, the most common BCG strain continues to be the Danish strain, despite its worldwide manufacturing interruption in 2015. Substantial variation and disproportionality exists in which regions were most affected by stockouts between 2009 and 2019. Tracking and understanding the reasoning behind changes to national BCG practices and their impact on TB burden is critical for decision makers as they contemplate how to include BCG vaccination in future immunisation guidelines in low and high TB burden countries.