The body is susceptible, yes.

[He pauses to cough again, more violently, leaning forward unsteadily in his seat until he can find his voice again.]

But my grace--part of my true self--should be healing and maintaining it. It isn't, entirely.

[He still doesn't have to breath, or eat, but he's having difficulty maintaining the vessel even in those basic things, let alone fighting off some sort of illness.]