Answer
Workers
Explanation:
The protection toward 'Vulnerable persons' according to The Common Rule (45 CFR 46, Sub part A) refers to the type of protection granted to Researches subjects that are not in their prime physical mental conditions. (For example, pregnant women or underage subjects)
'Workers' tend to be in adult age (older than 18) ,and considered to be healthy and psychologically sound (otherwise they will not be hired by their employers). Therefore, this group is not considered as 'vulnerable persons' and do not have specific protection form the common rule.