Abstract
Viral respiratory infections, including influenza, respiratory syncytial virus (RSV), and SARS-CoV-2, remain major global health challenges due to their high morbidity and mortality. Emerging evidence highlights the pivotal role of the gut-lung axis in regulating pulmonary immunity. The gut microbiota communicates with the lungs via endocrine, immune, and neuroimmune pathways-particularly through metabolites such as short-chain fatty acids (SCFAs) and vagus nerve-mediated signaling-which modulate immune cells including alveolar macrophages and dendritic cells. Disruption of gut microbial balance has been linked to impaired pulmonary immune responses and increased susceptibility to infection. This review synthesizes findings from animal models and clinical studies, demonstrating that interventions such as probiotics (eg, Lactobacillus gasseri), prebiotics (eg, galacto-oligosaccharides), fecal microbiota transplantation (FMT), and Traditional Chinese Medicine (eg, Astragalus, curcumin) can enhance antiviral cytokine production, restore gut-lung homeostasis, and reduce lung inflammation. For example, FMT from H7N9-survivor mice improved influenza resistance in recipients, and oral probiotics reduced respiratory failure risk in COVID-19 patients. These findings suggest that gut-lung axis modulation is a promising adjunctive approach for treating viral respiratory infections. Future research should prioritize personalized microbiome-based therapies and large-scale clinical trials to validate efficacy and safety.