In total, virus-positive patients showed a: bacterial richness; Actinobacteria, Bifidobacterium, Streptococcus, and Collinsella genera; Proteobacteria, Bacteroidetes, Enterobacteriaceae, and Bacteroides genera. Patients with severe COVID-19 exhibited: blood levels of inflammatory markers; CD8+ T cell number; abundance of F. prausnitzii and Roseburia. The gene discussed is CD8A; the disease is COVID-19.