Severe SARS-CoV-2 infection complicated by pneumonia is characterized by a shift towards the pro-inflammatory phenotype with an increase in IL-1a, FLT-3L, IL-2, IL-6, IL-9, MCP-3, IFNy, IL-5, Eotaxin, IL-12(p40), MDC, IL-17A, MCP-1, and IL-15, and on the part of the fecal microbiome, with dominance of Bacteroides, Feacalibacterium, and Prevotella_9 and a reduction in Haemophilus, Leptotrichia, Prevotella, Prevotella_7, Neisseria, and Streptococcus. The gene discussed is FLT3LG; the disease is susceptibility to pneumonia measurement.