Fig. 4.

The structure of SARS-CoV-2 genome and its variants. The genome of SARS-CoV-2 consists of ORF1a, ORF1b, and structural genes. While NSP3 and NSP5 of ORF1a encode papain-like protease and 3CL protease respectively, NSP12 and NSP13 of ORF1b encode RNA polymerase and helicase, respectively. The structural genes are responsible for the spike (S), envelope (E), membrane (M), and nucleocapsid (N) encoding. The spike-encoding region consists of two general regions S1 and S2 where the majority of mutations are related to this part. As illustrated, SARS-CoV-2 is categorized into different lineages based on the presence of mutations. Each bunch of mutations could give the SARS-CoV-2 various pathogenicity capacities letting variants have different transmissibility and severity.