Gweryina, R. I., C. E. Madubueze, and M. A. Nwaokolo. “Mathematical Modelling and Control of COVID-19 Transmission in the Presence of Exposed Immigrants”. Communication in Biomathematical Sciences, vol. 4, no. 2, Dec. 2021, pp. 93-105, doi:10.5614/cbms.2021.4.2.2.