Researchers published a study in Nature Communications identifying a nucleocapsid (non‑spike) mutation, denoted XEC, that increases SARS‑CoV‑2 pathogenicity in experimental models. The team led by Tsujino, Tsuda and Deguchi traced the mutation’s effects on viral replication dynamics and host immune responses, finding enhanced disease severity compared with reference strains. The work expands focus beyond spike‑protein adaptations by demonstrating how nucleocapsid changes can modulate virulence and host interaction. Authors caution that population‑level implications depend on mutation prevalence and interplay with immune history; they recommend genomic surveillance incorporate non‑spike loci to better detect variants with altered clinical impact.