friend of mine (early 20s) got his atp production severely damaged (not annihilated but way less than normal).

he can't really use stairs, or walk a long time, etc. he sleeps a lot, and basically can't be active for a long time anymore. his reaction time also worsened apparently (used to be ridiculously fast).

hospital folks (in 2 different countries) directly linked it to the vaccine.

so yeah it's rare but it can get really bad...