Modeling Complex Systems: A Case Study of Compartmental Models in Epidemiology

Figure 7

Time series of daily new COVID-19 infections from Sweden shows an epidemic plateau in April and May 2020. In the absence of sharp policy/behavioral changes, a homogeneous compartmental model cannot account for such an early plateau, which was clearly not the result of population-wide herd immunity. In a heterogeneous model, such a plateau could be partially explained by substantial immunity within the specific subpopulations that were responsible for the initial exponential growth. Epidemic data were obtained from refs. [64, 65].