The nose is the main entrance for respiratory viruses. These viruses are present there in an early stage and affect its function in terms of breathing and air humidification. The high percentage of COVID-19 patients diagnosed with anosmia highlight the primordial role of the nasal cavity in the physiopathology of respiratory viral infections. Mucus is the primary defense against viral infections. This physical barrier crucial in viral clearance is well known in the lung, unlike the nasal cavity where it has been little studied. The aim of our study is to elucidate the role of nasal mucociliary clearance in experimental mouse models of infection with the human syncytial virus and the SARS-CoV-2. We will use mice deficient for the two gel-forming mucins Muc5b and Muc5ac. We will study the diffusion of viruses in the nasal cavity, anosmia, cell damage, inflammation, localization of viral mimetics and the molecular mechanisms involved by molecular methods routinely performed completed by RNA-Fish and single-cell RNAseq.