Several theories have been proposed. Some researchers believe the amount of virus that infects an individual may have crucial outcomes. Get a huge dose and your outcome may be worse. Others argue that genetic susceptibility may be involved: in other words, that there are individuals whose genetic makeup leaves them more vulnerable to the virus as it spreads through their bodies.
In some cases, previously undiagnosed conditions are later revealed but in others no such explanations are available, leaving scientists struggling to find reasons for the behavior of the corona-virus.