A fractional-order delay dierential SEIR model for COVID-19: Stability analysis and Hopf bifurcation. Nonlinear Studies, [S. l.], v. 29, n. 2, 2022. Disponível em: https://nonlinearstudies.com/index.php/nonlinear/article/view/2478. Acesso em: 13 sep. 2025.