The coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)1. Detection of the virus was first reported in Wuhan2, China and has since spread worldwide, emerging as a global pandemic3.
In symptomatic patients, nasal swabs have yielded higher viral loads than throat swabs4. The same distribution was observed in an asymptomatic patient4, implicating the nasal epithelium as a portal for initial infection and transmission. Cellular entry of coronaviruses depends on the binding of the spike (S) protein to a specific cellular receptor and subsequent S protein priming by cellular proteases. Similarly to SARS-CoV5,6, SARS-CoV-2 employs ACE2 as a receptor for cellular entry. The binding affinity of the S protein and ACE2 was found to be a major determinant of SARS-CoV replication rate and disease severity4,7. Viral entry also depends on TMPRSS2