Alliance for Pandemic Preparedness

May 15, 2020

Time Is of the Essence Impact of Delays on Effectiveness of Contact Tracing for COVID-19

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  • Researchers modeled the impact of delays in contact tracing strategies (CTS) and found that testing delay (time between onset of symptoms to testing and diagnosis) could seriously attenuate any contact tracing efforts. A testing delay of 3 days would require contacts to be traced within 1 day and with 80% coverage to keep the effective reproduction number (R) below 1. A testing delay of 4 days would prevent the R from going below 1 even with the most efficient CTS (0 tracing delay, 100% coverage). 
  • The findings also highlight the effectiveness of app-based contact tracing and estimates indicate that even with only 20% coverage, it is superior to conventional contact tracing.  
  • This model assumes a baseline R of 1.2, no transmission in healthcare settings, and that all index cases and contacts no longer transmit the virus. 

Kretzschmar et al. (May 15, 2020). Time Is of the Essence Impact of Delays on Effectiveness of Contact Tracing for COVID-19. Preprint downloaded May 15 from https://doi.org/10.1101/2020.05.09.20096289