  The dynamics of many epidemic models for infectious diseases that spread in a
single host population demonstrate a threshold phenomenon. If the basic
reproduction number R0 is below unity, the disease-free equilibrium P0 is
globally stable in the feasible region and the disease always dies out. If R0 >
1, a unique endemic equilibrium P? is globally asymptotically stable in the
interior of the feasible region and the disease will persist at the endemic
equilibrium if it is initially present. In this paper (Part I), we
reinvestigate the study of the stability or the non stability of a mathematical
Covid-19 model constructed by Nita H. Shah, Ankush H. Suthar and Ekta N.
Jayswal. We use a criterion of Li-Wang for stability of matrices [Li-Wang] on
the second additive compound matrix associated to their model. In second paper
(Part II), In order to control the Covid-19 system, i.e., force the
trajectories to go to the equilibria we will add some control parameters with
uncertain parameters to stabilize the five-dimensional Covid-19 system studied
in this paper. Based on compound matrices theory, we apply in [Intissar] again
the criterion of Li-Wang to study the stability of equilibrium points of
Covid-19 system with uncertain parameters. In this part II, all sophisticated
technical calculations including those in part I are given in appendices.
