“Or serious issues” is doing a lot of work in the headline. Some of these athletes suffered things like groin injuries, bacterial infections, cancer, aneurysms, or one of many other things. Some of them weren’t remotely young. I didn’t see any mention of COVID vaccination in any of the cited stories I checked, so I can’t tell who was or wasn’t vaccinated, or if they were, when. It’s not obvious to me there was any common cause.