A time-delayed model for the spread of COVID-19 with vaccination.

A mathematical model is presented in this paper to investigate the effects of time delay in vaccine production on COVID-19 spread. The model is analyzed qualitatively and numerically. The qualitative analysis indicates that the system variables are non-negative, bounded, and biologically meaningful. Moreover, the model has produced two equilibrium points: the free equilibrium point, which can exist without conditions, and the endemic equilibrium point, which can exist if the control reproduction number, R c , is not less than one. In addition, the local stability of the equilibrium points is investigated and agrees with the numerical analysis results. Finally, a sensitivity analysis is conducted for R c . In particular, we examine the effect of the vaccine's time delay, vaccine rate, and vaccine efficiency on the model dynamics. [ABSTRACT FROM AUTHOR]