Respiratory tract mucus is a complicated combination of water (∼95%), inorganic salts (∼1%), and various macromolecular organic compounds including glycoproteins (i.e., mucins) and lipids [20], [21], [32]. It has been shown to be protective for IAV at low RH [33], [34]. However, the relationship between viability of IAV in mucus and RH is still not completely clear.