My partner's best friend is hospitalized this Christmas with the long term affects of covid. He was fit, cross country runner since high school and still was running decades later. He got covid in 2020, almost died and has been sick ever since. He was hospitalized for months in 2020. Even after he was released he was unwell. He couldn't even walk.
I am betting he would be healthier now had he opportunity to be vaccinated. Of course, there was no vaccine then. The point being, covid can be a life threatening condition, even if the individual is fit and in good health otherwise.