An analytic approximate solution of the SIR model

Lazzizzera, Ignazio

The SIR(D) epidemiological model is defined through transcendental equations not solvable by elementary functions. In the present paper, those equations are successfully replaced by approximate ones, whose solutions are given explicitly in terms of elementary functions, namely, piece-wisely, generalized logistic functions: they unveil a useful feature, that in fact is also owned by the (numerical) solutions of the exact equations.