This paper presents the determination of the transfer function of the spreading pandemic caused by SARS-CoV-2 in different countries. The methodology of system identification, well known in control system theory, based on the number of infected was used. Appropriate hypotheses have been adopted to determine the transfer function of the system. Each country is viewed as a separate system, and comparisons of determined systems are given. The systems are also presented in the state space, the stability of the systems is analysed, and the matrices of controllability and observability are determined. After analysis, it is shown that the spread of the SARS-CoV-2, for each country, can be described with the same order of transfer function and differential equation.