Anecdotal, but my wife is an avid cyclist and rides with a girl who is a 20+ year ICU nurse in Chattanooga. This girl has been dealing exclusively and directly with COVID patients for a year and a half in the ICU ward. She says nearly the exact same thing as the nurse in this article. I’ve heard almost those exact words come out of her mouth first hand. She tells me the sickest of the sick she’s seen in her ICU are people who are “fully vaccinated”. One other thing she tells me they’ve noticed, but I’ve not seen reported anywhere, is the sickest of the sick tend to have A-type blood.
I don’t know about severity, but I remember seeing something a while ago that frequency varied by blood type and rH factor. I think A was higher.