In the paper, the authors put two drug strains under various levels of competition and establish that cross‐immunity and host isolation lead to periodic epidemic outbreaks in the multistrain system. For the model, by the reproduction number of strain one, scriptR1, and the reproduction number of strain two, scriptR2, they show local and global stability and backward bifurcation under suitable conditions.

<p style='text-indent:20px;'>In this paper, we analyze a mathematical model of the SIER type which includes susceptible and infected and removed people. In this model, we compute <inline-formula><tex-math id="M1">\begin{document}$ {\mathcal{R}_1} $\end{document}</tex-math></inline-formula> in strain one and <inline-formula><tex-math id="M2">\begin{document}$ {\mathcal{R}_2} $\end{document}</tex-math></inline-formula> in strain two. Then we compute the equilibrium points and then determine the global stability.</p>