Epidemiological systems are complex because they involve: 1. Multiple Interacting Agents: Individuals, pathogens, vectors, and environments. 2. Dynamic Interactions: Continuous changes in disease patterns and host-pathogen interactions. 3. Feedback Loops: Mechanisms where the output of a system can influence its own input, such as immunity development or changes in behavior due to public health interventions. 4. Heterogeneity: Variability in populations concerning susceptibility, behavior, and social networks.
