Transmission Waiting Time: A Unifying Metric for Outbreak Controllability

Traditional outbreak containment strategies—such as isolating symptomatic individuals and tracing their contacts—often fall short for pathogens with substantial pre-symptomatic or asymptomatic transmission, as exemplified by SARS-CoV-2. This challenge was met by technological advances during the COVID-19 pandemic: widespread, low-cost molecular testing enabled population-scale screening independent of symptoms, while digital tools such as mobile exposure notifications and backward contact tracing improved the speed and precision of response efforts. These advances redefined the landscape of non-pharmaceutical interventions, shifting the focus from symptom-based interventions to proactive, testing-driven identification and isolation of infections.

Here, we introduce a theoretical framework centered on the transmission waiting time—the interval between an individual’s infection and their first onward transmission—as a critical benchmark for outbreak control. This framework integrates key pathogen properties, such as the basic reproduction number ( R ₀ ) and the generation interval, with operational parameters including the speed and coverage of isolation. We analytically derive the transmission waiting time distribution under a homogeneous mixing assumption and extend the framework to incorporate transmission heterogeneity, demonstrating its utility in establishing temporal thresholds for effective containment.

Applying this framework across a wide range of pathogens reveals substantial variation in controllability, with pathogens that are highly transmissible and/or have shorter generation intervals placing stricter demands on the speed and reach of interventions. Simulation-based analyses further underscore the necessity of optimizing both the timeliness and coverage of isolation efforts.

Taken together, our framework provides clear, biologically grounded metrics for guiding epidemic containment strategies, offering flexible and scalable benchmarks tailored to modern public health response capabilities.