The investigations performed by Lu et al. by optical coherence tomography via bronchoscopy on critically ill COVID-19 patients indicated heightened levels of the mucins MUC5AC, MUC1 and MUC1-CT; notably, MUC1 is a membrane-anchored mucin expressed on the apical surface of the airway epithelial cells, while MUC1-CT is expressed on the cytoplasmic side of these cells [8]. Here, MUC5AC is linked to COVID-19.