The viral load of Delta variant patients is very high. It shows that the replication activity of the Delta variant of the SARS-COV-2 virus is very active. The viral proteins directly related to viral replication activities are orf1ab and N proteins. We searched the orf1ab and N protein mutation sites of five variants of Alpha, Beta, Gama, Delta, and Lambda from "CORONAVIRUS CORONAVIRUS ANTIVIRAL & RESISTANCE DATABASE" ( . stanford. edu/ page/ mutation-viewer). Then compared with Table to find the MHC-like enhanced region sites of orf1ab and N proteins (Table ). Table shows that the orf1ab and N protein mutation sites of Alpha, Beta, and Gama variants are not in the MHC-like region. The N protein mutation site of the Lambda variant is also not in the MHC-like area. However, the mutation sites of Delta (orf1ab and N protein) and Lambda (orf1ab protein) are in the MHC-like region. The RdRP: G671S mutation site of Delta variant orf1ab is at MHC_I-like_Ag-recog C. The nsp3:F1569V of Delta variant orf1ab is at MHC_II_beta B and MHC_I-like_Ag-recog E. The D63G of Dalta variant N is in MHC_II_beta A, MHC_I-like_Ag-recog A. Both N and RNA-dependent RNA polymerase are directly related to virus replication. In addition, the interaction between N and Nsp3 is essential for connecting the viral genome for processing. So, table 7 indicates that the mutations of RdRP: G671S and N: D63G enhanced the immune escape ability of the Delta variant virus during the replication process.Therefore, the replication activity for this variant is very active