DPP4 expression in the nasal epithelium of the camel, llama, and pig allows them to develop upper respiratory tract infection upon intranasal inoculation with MERS-CoV2,9,26, while in humans, DPP4 is exclusively expressed in the lower respiratory tract epithelium, which is in line with acute pneumonia being the main clinical outcome of MERS-CoV infection26,27. Here, DPP4 is linked to Recurrent upper respiratory tract infections.