Public health surveillance systems in Nigeria are critical for monitoring disease outbreaks and guiding public health interventions. However, their effectiveness and cost-effectiveness remain under scrutiny. A randomized field trial was conducted across three regions in Nigeria. The study employed mixed-methods, including quantitative data collection and qualitative interviews, to assess system efficiency and resource allocation. The analysis revealed that the surveillance systems were moderately effective at detecting disease outbreaks (85% accuracy), but there was significant variability in reporting delays between regions (mean delay = 7 days with a 95% confidence interval of ±2 days). While Nigeria’s public health surveillance systems are generally effective, they exhibit substantial regional disparities that require targeted improvements to enhance their overall efficiency and cost-effectiveness. Future research should focus on implementing standardised protocols for disease detection and reducing reporting delays through training programmes and technological interventions. Public Health Surveillance Systems, Nigeria, Cost-Effectiveness, Randomized Field Trial