Effectiveness of isolation, testing, contact tracing and physical distancing on reducing transmission of SARS-CoV-2 in different settings

Abstract

Background: Isolation of symptomatic cases and tracing of contacts has been used as an early COVID-19 containment measure in many countries, with additional physical distancing measures also introduced as outbreaks have grown. To maintain control of infection while also reducing disruption to populations, there is a need to understand what combination of measures -including novel digital tracing approaches and less intensive physical distancing -may be required to reduce transmission.Methods: Using a model of individual-level transmission stratified by setting (household, work, school, other) based on BBC Pandemic data from 40,162 UK participants, we simulated the impact of a range of different testing, isolation, tracing and physical distancing scenarios. As well as estimating reduction in effective reproduction number, we estimated, for a given level of COVID-19 incidence, the number of contacts that would be newly quarantined each day under different strategies.Results: Under optimistic but plausible assumptions, we estimated that combined testing and tracing strategies would reduce transmission more than mass testing or self-isolation alone (50-65% compared to 2-30%). If limits are placed on gatherings outside of home/school/work (e.g. maximum of 4 daily contacts in other settings), then manual contact tracing of acquaintances only could have a similar effect on transmission reduction as detailed contact tracing. In a scenario where there were 10,000 new symptomatic cases per day, we estimated in most contact tracing strategies, 140,000 to 390,000 contacts would be newly quarantined each day. Conclusions:Consistent with previous modelling studies and country-specific COVID-19 responses to date, our analysis estimates that a high proportion of cases would need to self-isolate and a high proportion of their contacts to be successfully traced to ensure an effective reproduction number that is below one in the absence of other measures. If combined with moderate physical distancing measures, self-isolation and contact tracing would be more likely to achieve control.

Bidirectional contact tracing dramatically improves COVID-19 control

“…Epidemiological parameters for COVID-19 remain highly uncertain. Among these, R0 has both wide ranges in published estimates (4,10,(26)(27)(28)(29) and is expected to have large effects on outbreak outcome. To evaluate the robustness of our findings, we repeated our analysis of different contact-tracing approaches under R0 values ranging from 1.0 to 4.0 ( Fig.…”

Covasim: an agent-based model of COVID-19 dynamics and interventions

“…Additionally, agent-based models have been developed to evaluate the impact of social distancing and contact tracing (Aleta et al, 2020;Kretzschmar et al, 2020;. Features of these models include accounting for the number of household and non-household contacts (Chao et al, 2020;Kretzschmar et al, 2020;Kucharski et al, 2020); the age and clustering of contacts within households (Aleta et al, 2020;Chao et al, 2020;Kucharski et al, 2020); and the microstructure in schools and workplace settings informed by census and time-use data (Aleta et al, 2020). Branching process models have also been used to investigate the impact of non-pharmaceutical intervention strategies (Hellewell et al, 2020;Peak et al, 2017).…”

Facilitators and barriers to engagement with contact tracing during infectious disease outbreaks: A rapid review of the evidence

“…Until a vaccine is developed, a test, trace and isolate strategy is the most effective method of controlling the COVID-19 outbreak [ 2 – 4 ]. This system is heavily reliant on members of the public engaging with it.…”