COVID-19 disease is a consequence of low immunity. Low immunity is the cause of COVID-19 disease.
Not all people exposed to COVID-19 get infected. Those that have optimal immunity experience none or mild symptoms temporarily. Only those having low immunity are seen to experience a gradual progression from mild-moderate symptoms to serious symptoms & life-threatening respiratory conditions.
Diseases of COVID-19 infection are seen to be a consequence of low immunity. Therefore, low immunity is the cause to COVID-19 diseases.