Experimental Models to Investigate Viral and Cellular Dynamics in Respiratory Viral Co-Infections.

Respiratory viral co-infections by viruses such as influenza virus, SARS-CoV-2, and respiratory syncytial virus (RSV) are a significant clinical issue in high-risk populations such as children, elderly patients, and immunocompromised individuals. Sequential and simultaneous co-infections exacerbate disease severity, leading to acute respiratory distress syndrome (ARDS), prolonged hospitalization, and increased mortality. Molecular and immunological interactions are complex, context-dependent, and largely unknown. Experimental models of infection that accurately mimic human respiratory physiology are required for the study of viral dynamics, virus-virus interactions, and virus-host interactions. This review outlines a range of complex in vitro and ex vivo models, including organoids, air-liquid interface cultures, lung-on-a-chip platforms, and in vivo animal models, highlighting their ability to simulate the complexity of respiratory co-infections and their limitations. The field has developed significantly, despite challenges like variability across viral strains, timing of infection, and non-standardization of models. Integration of multi-omics technologies and application of highly translational models such as non-human primates and lung-on-a-chip technology are promising avenues to uncover the molecular determinants of co-infection and guide development of targeted therapeutic strategies. Interrelatedness of experimental models and clinical outcomes is highly critical to improve prevention and treatment of respiratory viral co-infections mainly among high-risk populations.