Table 5.
Specific contact tracing interventions which can achieve epidemic control / extinction (R ≤ 1) from additional studies included in the review
| Studies not modelling contact tracing in reopening scenarios after 2020 lockdown | Studies modelling contact tracing in reopening scenarios after 2020 lockdown | |
|---|---|---|
| Manual forward tracing of primary contacts (including educational institutions) |
- Contact tracing (90%, time to trace 0.5 days) and 90% effective quarantine [80] *** Without other interventions, R < 1 - Isolation and contact tracing with 20% of undetected cases and strong social distancing [89] *** R < 1 - Contact tracing and isolation (90%) with low transmission (R = 1.5) but 40% of transmission asymptomatic [77] *** less than 20% probability of R < 1 - Contact tracing with high [medium-low] transmission efficiency + contact tracing (80-100%) [60-100%] + high [medium] contact testing capacity [40] *** R < 1 - Case isolation + contact tracing (90%) + mask wearing + physical distancing [79] *** R < 1 as long as with physical distancing R = 1.2 - Mass random testing (10%) + contact tracing (50%/100%) with/without social distancing [67] *** R < 1 - With pre-symptomatic transmission and low (R = 1.5)/ high (R = 2.5) infectivity and time to trace delay of 3.5 days, contact tracing (80%) [74] *** R < 1 |
- Testing of symptomatic individuals and asymptomatic contacts (90%) + contact tracing (90%) + social distancing [58] *** R < 1 - Full-time [part-time] school reopening with symptomatic testing 75% [65%] and contact tracing with 68% [40%] coverage + some social distancing [52] *** R < 1 - Case isolation and contact tracing after lifting of lockdown (R = 2.7) [75] *** R < 1 with early isolation and 100% of contacts traced |
| Digital or hybrid (manual + digital) contact tracing |
- Isolation of cases with two-day delay + digital contact tracing (20% app adoption) + 50% quarantine efficacy + physical distancing (R = 1.2) [84] *** R < 1 - With high pre-symptomatic infectiousness, case isolation and contact tracing (60%) + high efficiency mask wearing (50%) + social distancing (R = 1.5) [72] *** R < 1 - Combination of lockdown and digital contact tracing (60% of population owns smartphones) [57] *** R < 1 - Digital contact tracing (40-60%) + time to trace 0 days + low (30%) probability of transmission [90] *** R = 1 - Digital contact tracing (90%) [80%] with time to trace = 0 days and 80% of symptomatic detected without/ with reduction in transmission [54] *** R < 1 |
- Digital contact tracing with 26% app adoption + physical distancing (20%) [7] *** R = 1 |
| Delays to contact tracing |
- Isolation of symptomatic + contact tracing with no social distancing [85] *** R < 1 if time to trace < 3 days + high success in quarantining contacts and isolating cases. R < 1 with time to trace = 0 and 70% success of quarantining contacts/ cases - Test symptomatic (80%) with a testing and tracing delay of 0 days and 80% contact tracing coverage [8] *** R < 1 - Contact tracing with 100% coverage of household contacts and no social distancing [78] *** time to trace must be at most one day for R < 1 - Delay to isolation of symptomatic (1 day) + highly successful contact tracing (3 asymptomatic detected per symptomatic) + physical distancing (R = 2) [82] *** R < 1 - Increasing contact tracing coverage (50-80%) compared to reducing time to trace from four to one days [68] *** Increasing contact tracing coverage is more effective than reducing time to trace |
- With a test capacity of 2.7 thousand per day, contact tracing (70%) + time to trace = 2 days + mask wearing and school closures [45] *** R < 1 |
| Backward or bidirectional contact tracing | - Contact tracing of symptomatic considering household structure and physical distancing (50%) / Backward digital contact tracing of individuals (50%) [73] *** R < 1 / Reduces growth rate if recall does not decay |