RWAT, S. I.; AHMAD, N. A. A. Backward Bifurcation and Hysteresis in a Mathematical Model of COVID19 with Imperfect Vaccine. MATEMATIKA: Malaysian Journal of Industrial and Applied Mathematics, [S. l.], v. 39, n. 1, p. 87–99, 2023. Disponível em: https://matematika.utm.my/index.php/matematika/article/view/1458. Acesso em: 30 may. 2023.