Koch’s 4 postulates apparently cannot be applied to a virus

I wish to share a correction that may burst some people’s bubbles.
 
Koch’s 4 postulates apparently cannot be applied to a virus as a virus cannot grow without being in a cell.
 
https://www.auckland.ac.nz/en/news/2020/11/16/kochs-postulates-covid-and-misinformation-rabbit-holes.html
 
But the elephant in the room that main stream medicine and the media almost completely ignore is this gem:
 
“many microbes can live in and on people and only cause disease under certain circumstances”
 
Which is what we are observing with COVID. The vast majority of the deaths are in people with comorbidities!
 
So where is the race to determine how to help us all get healthy so we are more infection resistant?