Furthermore, we assume that the total population size, denoted as N, is constant and can be normalized to S͑t͒ + E͑t͒ + I͑t͒ + R͑t͒ = 1, where S͑t͒ = s͑t͒ / N, E͑t͒ = e͑t͒ / N, I͑t͒ = i͑t͒ / N, and R͑t͒ = r͑t͒ / N. Therefore, the population class variables S, E, I, and R represent fractions of the total population. The governing equations for the stochastic SEIR model are Schematic demonstrating the injection of a common noise into both the high-dimensional system and its associated low-dimensional system.