Answer:
Workers
Step-by-step explanation:
The protection toward 'Vulnerable persons' in this context is given to Researchers subjects that are not in their prime physical or psychological conditions. (Such as pregnant women or underage subjects)
Workers because People who are categorized as workers tend to be in adult age (older than 18) ,and considered to be healthy and psychologically sound (otherwise they will not be hired). Therefore, this group is not considered as 'vulnerable persons'