Residents and Interns--{Physicians in Training)make up a large part of the medical workforce of many "teaching hospitals". They are typically overworked to begin with, perform many of the unpleasant  but necessary tasks(i.e. "scut") that the attending physicians are above doing, and would be exceedingly difficult to replace in an emergency.  For the most part they are also smack dab in the center of the demographic that develops cytokine storm, which means that once they go down many of them may well stay down permanently.