1. I am not familiar with coronavirus biology, however, as to the general question about nasal -> brain routes if infection: yes this is a risk if the virus is

1. I am not familiar with coronavirus biology, however, as to the general question about nasal -> brain routes if infection: yes this is a risk if the virus is able to infect the olfactory nerves and travel retrograde through the cribriform plate into the olfactory bulb. It is a little peculiar that it would lead to medullary viral replication, as the medulla is a few steps back and distal from the olfactory bulb. Other infectious agents can travel into the CNS via the cribriform plate, most terrifying is naegleria fowleri but other terrible fungal infections like mucor and rhizopus can do it as well. They don’t tend to grow in neurons but rather eat through the tissues. 2. Upper versus lower: when people have a URI the upper airways meaning the nasopharyngeal, oropharyngeal, and trachea are predominantly affected. The typical symptoms are runny nose, nasal congestion, sore throat. However, SARS/COVID tends to cause a lower respiratory syndrome affecting the small airways deep in the lungs, namely the alveoli and small bronchioles. It is entirely consistent to hypothesize that infection through the upper airway mucosa is “worse” but the target cells that primarily cause disease are in the lower airway.