Abstract: "SARS-CoV-2 and, to a lesser extent, influenza A can lead to long-term complications in the respiratory and nervous systems. However, the mechanisms driving post-viral sequelae remain poorly understood. To address this gap, we longitudinally characterized C57BL/6 mice infected with sublethal doses of mouse-adapted SARS-CoV-2 (MA30) or influenza A (PR8). Lung and brain tissues were analyzed at 14-, 21-, and 28-days post-infection (DPI) using histological analysis and bulk-RNA sequencing. In the lungs, both infections caused prolonged inflammation and fibrosis. MA30-infected lungs showed persistent upregulation of inflammationory, coagulation, complement, as well as fibrotic, and extracellular matrix (ECM) remodeling pathways at 21 DPI, alongside downregulation of epithelial junction and metabolic program pathways. In contrast, PR8-infected lungs exhibited a strong acute interferon response and chronic upregulation of basal epithelial markers (e.g., Krt5, Krt14), consistent with epithelial regeneration. Notably, only PR8-infected mice displayed KRT5+ progenitor cell migration into damaged lung regions, indicating divergence in repair mechanisms. Neither MA30-infected, nor PR8-infected mice had detectable brain infection. However, MA30 mice, but not PR8-infected mice exhibited an elevated frequency of microhemorrhages at early timepoints and marked neuroinflammation at all timepoints. Transcriptomic profiling of MA30-infected brains showed enrichment for up-regulation of ECM remodeling, vascular dysfunction, IL6-signaling pathways along with a virus-specific disruption of the hypothalamic–pituitary axis with MA30 infection not seen in PR8-infected brains. These included genes linked to neuroinflammation, sensory processing disruption, and microvascular injury, mirroring clinical features of Long COVID. Together, these findings establish distinct tissue-specific trajectories of long-term pathology following SARS-CoV-2 and influenza infection and provide a foundation for dissecting the mechanisms of post-viral lung and brain disease."