“…According to the above description, the involved model is a standard SIS/logistic one, with external infection and the additional feature that some of the population is initially vaccinated, with imperfect immunity. More specifically, mathematical model was introduced in the paper
31 as a compartmental model that, at any particular instant
, classifies individuals as susceptible
, vaccinated
, or infected
. Figure 1 represents the movement of individuals among the three epidemiological classes.…”