Vaccination and time limited immunization for SARS-CoV-2 infection

The paper aims at a discussion of the effects of the containment measures against COVID-19 through the analysis of the reproduction number. Starting from a mathematical model in which several controls are considered, including the vaccination, and introducing also an hypotised limited duration of the immunity acquired both from vaccine and from healing from the illness, the steady state behaviour, both in the uncontrolled and in the controled cases is studied. The expressions for the basic reproduction number and the actual reproduction number under control actions are computed by means of the next generation matrix approach. This function is numerically investigated, showing some graphs which illustrate, qualitatively and quantitatively, in an intuitive way the positive effects of the controls and the negative contribution of the absence of a lifetime immunization from virus.