Implication of backward contact tracing in the presence of overdispersed transmission in COVID-19 outbreaks

Introduction: Contact tracing has the potential to control outbreaks without need for stringent physical distancing policies, e.g. civil lockdowns. Unlike forward contact tracing, backward identifies source of newly detected cases. This approach is particularly valuable when there high individual-level variation in number secondary transmissions (overdispersion). Methods: By using a simple branching process model, we explored combining with more conventional COVID-19. We estimated typical size clusters that can be reached by and simulated incremental effectiveness tracing. Results: Across ranges parameter values consistent dynamics SARS-CoV-2, expected identify primary case generating 3-10 times infections than randomly chosen case, typically increasing proportion subsequent cases averted factor 2-3. The became greater higher degree overdispersion. Conclusion: Backward an effective tool outbreak control, especially presence overdispersion as observed SARS-CoV-2.