Chemical Master Equation model to predict the COVID-19 epidemic spread

The COVID-19 pandemics has shown relevant stochasticity in the spread of viral in- fection. Here, we formulate the dynamics of the epidemics spread as a stochastic SIR model, handling the compartmental model (of the SIR type) as a set of chemical reactions, and applying the Chemical Master Equation that describes the dynamics of the equivalent stochastic chemical reaction system. In this way, the solution (evolution of the probability distribution over time) can be obtained via the classical Stochastic Simulation Algorithm. The proposed methodology has been used to predict the COVID-19 evolution in small and medium size municipalities of Galicia.