The potential HCV resistance against DAA drugs is a concern. Among the HCV quasispecies there are pre-existing variants with the potential to confer resistance to NS5A inhibitors without having any previous exposure to those drugs. Generally, the replication of these variants happens only in minute quantities, making them undetectable by current techniques. On the other hand, it is possible to selectively grow immune variants in the presence of NS5A inhibitors. HCV resistance is characterized by a certain escape pattern. This pattern is often associated with amino acid substitutions that confer upon the virus a robust drug resistance without impairing the viral fitness. It has been established that NS5A inhibitors possess a relatively low threshold for resistance, and variants that are associated with NS5A resistance have been shown to endure for up to six months in patients following treatment cessation. Therefore, combination therapies produce higher efficacy and shorter treatment periods.