Final answer:
The subject of this question is Health, and it is about the requirement of employers to offer a free vaccine to protect CNA's from a specific infection, presumably Hepatitis B.
Step-by-step explanation:
The subject of this question is Health. The question is asking about the requirement of employers to offer a free vaccine to protect Certified Nursing Assistants (CNA's) from something, but the information provided is incomplete. However, based on the information provided about preventing HBV transmission in healthcare settings, it can be inferred that the question is related to the vaccination of CNA's against Hepatitis B.