Evidence for the dependence of the SARS-Cov-2 Delta high diffusivity on the associated N:G215C nucleocapsid mutation

The continuous evolution of the SARS-CoV-2 virus genome and the consequent substitutions observed in the amino acid sequences, can induce significant changes in parameters such as diffusivity and pathogenicity, and causes constant concern regarding the efficacy of vaccines against the new variants in circulation. In recent months there has been an increase in the number of infections first in India, and more recently in the United Kingdom. The genome sequencing of the samples showed that this increase coincided with the emergence of a new variant, B.1.617.2, also known as VOC Delta. This variant is rapidly becoming dominant in several countries, causing increasing concern for its extreme diffusivity and its ability to often overcome the vaccines. The high diffusivity of this variant is normally ascribed to the Spike protein mutations. However, we will show here that it is rather due to the nucleocapsid substitution N:G215C. This is made clear by comparing, in the genomic sequences available on the GISAID database, the relative increase of the Delta variant with and without the associated N:G215C substitution. Once the extreme diffusivity of the Delta variant with associated nucleocapsid aminoacidic substitution is evidenced, we tentatively explain it as possibly due to the adaptive effect of the highly selective environment in Countries with high levels of vaccination.