MUC5AC and viral infectious disease: Local mucosal processes caused by the viral infection—epithelial damage and cell loss, breakdown of mucin by viral neuraminidase, increased receptor availability on epithelial cells due to the promotion of augmented bacterial adherence, inhibition of phagocyte function and neutrophil NET functioning, abnormal expression of antimicrobial host defense peptides, and launching of local immunological processes [47,48,49].