MUC5AC and idiopathic pulmonary fibrosis: MUC5B polymorphisms are well known to be associated with the risk of idiopathic pulmonary fibrosis,26 and in a postmortem study of 21 patients who died after COVID‐19, both MUC5B and MUC5AC transcript levels were elevated in the subacute and chronic disease phases, and 93% of COVID‐19 lungs suitable for distal lung studies exhibited MUC5B‐driven mucus accumulation in distal airways.27