As of Feb. 2021, COVID-19 is still spreading. To overcome this infectious disease, COVID-19 vaccines are being developed around the world. In Japan, inoculation of COVID-19 vaccines to people will be starting soon (as of Feb. 2021). However, desirable vaccination strategies are not clear. Therefore, we investigate the relationship between vaccination strategies and COVID-19 spreading using positive-case data in Japan. The method is SIRVD (Susceptible Infected Recovered Vaccination Death) model, which can represent vaccinated persons. Moreover, we discuss desirable vaccination strategies based on the results.