So is it possible the serious outcome risk is even higher in the younger cohort? This is my thinking:

Younger folks are more likely to mount a stronger immune response and are less likely to show key signs and symptoms.

Someone who is 70 with a hemaglobin of 7.0 is going to be severely symptomatic and seek medical care. There is time for the doctors to intervene and get the health situation turned around.

That 20 something with a hemaglobin of 5.something doesn't show any symptoms. But for an urgent care visit for an unrelated health issue, he would have gone to sleep and not awakened.

I guess we are going to find out.

My other thought is that if a large group of people (say hospital employees) are vaxxinated all around the same time, the antibodies would all be wearing off around the same time. Mass illness?