Could covid not actually be just a disease? Maybe it's a disease + chronic unhealth. Due to age, pollution, obesity, bad diet, sitting on yr butt too much and/or etc
Nearly all diseases are worse if you're in bad health to begin with. That doesn't make them "not just diseases".
And there are a thousand species of varmint that inhabit our body without helping or hurting anyway.
So yes, massive unhealth can definitely spell the difference there.