Nconsidering nbac's analytic approach, an otherwise competent person who is acutely ill might be considered at especially high risk of harm for

The correct answer is situational cognitive vulnerability. 
This means that this particular person cannot perform his or her usual tasks as effectively as before because of some problem that may have come up in the meantime, or in this case, an acute illness. This illness is the situation which is preventing this person from doing their job as efficiently, which means they will be vulnerable 'situationally.'