Due to the lack of repairing mechanism of RNA virus replicase complex, SARS-CoV-2 mutations frequently occur during viral replication [111]. The genetic drifts of SARS-CoV-2 are a selective evolution toward less immunogenicity for host immune surveillance by T- or B-cells. The latter appearing strains are less immunogenic than earlier ones [113]. Antigenic drift is also reported in the COVID-19 pandemic. The highly prevalent 23403A > G (p.D614G) variant in the European population may result in vaccine mismatches with little protection to that group of patients [114,115].