Why are some COVID-19 infected people asymptomatic?

Immune cells in the lungs are important for the immune system’s recognition and fight against viruses. However, the virus that produces COVID-19 is not recognised by these cells, as the virus may hide its genomic material, and as a result the cells’ immune system against the virus is not activated. This may help explain why some people with COVID-19 are asymptomatic in the early stages of the disease. Source