Viruses Are Not New
Viruses have always existed and they continually evolve and change. So understanding how COVID-19 works in the human body is paramount. Some viruses like COVID-19 that have found their way into humans have caused great harm in recent decades —of course the new coronavirus but even its predecessors, SARS and MERS. This is also true for the virus that causes AIDS.
Therefore, the sequence of events below are what occurs when you come down with the flu or a cold and is a good demonstration of how the dangerous viruses we become infected with work as they jump from animals to humans.