Why is runny nose uncommon in COVID-19?
The secret of SARS-COV2 in COVID-19 lies in this simple observation. How can a viral infection which primarily infects the nasal passages not cause nasal congestion?
Runny nose has been reported in less than 5% of cases and is even lower than abdominal pain. (link in comments)
The primary cause of severe lung disease is a delayed interferon response to the virus. This is because the strategy employed by SARS-COV2 is to inhibit interferon production within infected cells.
It means, any coronavirus applied to the mucosa of nose will prime the body to produce interferon on exposure to the virus, causing a runny nose to prevent spread to the lungs and transmission to others.
Hit the virus at the weakest point.