Dr. Roger Seheult was showing the damage to the endothelial cells lining the vascular system in his COVID updates probably around April or May 2020.
Clots, Strokes And Rashes. Is COVID-19 A Disease Of The Blood Vessels?
He was probably observing side effects from Remdesivir:
https://www.drugs.com/sfx/remdesivir-side-effects.html