Evaluating the evolution of the timeliness of test-based surveillance systems over the course of a pandemic

1The timeliness of infectious disease surveillance systems largely determines the speed at which mitigation interventions may be implemented. However, it is unclear how surveillance timeliness evolves during a pandemic with changing government policies, testing tools, and population-level infection and immunity landscapes. Here, we adapt an agent-based model for COVID-19 transmission to explore the timeliness of the surveillance signals obtained from polymerase chain reaction (PCR) and rapid antigen (RAT) tests relative to true infection incidence. Across different pandemic scenarios, we investigate how surveillance timeliness depends on the prevalence of co-circulating influenza-like-illnesses (ILI) and test quality. If only PCR tests are available with symptom-based eligibility, and if tests can detect post-recovery residual viral load, then a surveillance lag may emerge which is amplified by ILI prevalence. When limited RATs are introduced with symptom-based eligibility, and PCR eligibility requires a recent positive RAT, then RAT/PCR timeliness is sensitive to ILI prevalence but insensitive to RAT failure probability. With unrestricted RAT supply, PCR timeliness varies with both ILI prevalence and RAT failure probability. Our work highlights how the timeliness of test-based surveillance signals can evolve throughout a pandemic, with important implications for interpreting real-time surveillance data and designing more effective, data-driven surveillance systems.