Rwat, Solomon Isa, and Noor Atinah Ahmad Ahmad. “Backward Bifurcation and Hysteresis in a Mathematical Model of COVID19 With Imperfect Vaccine”. MATEMATIKA 39, no. 1 (April 15, 2023): 87–99. Accessed April 20, 2024. https://matematika.utm.my/index.php/matematika/article/view/1458.