Final answer:
The muscle that should never be used for vaccines is the Biceps brachii.
Step-by-step explanation:
The muscle that should never be used for vaccines is the Biceps brachii.
When administering a vaccine, the deltoid muscle is typically used. This is because the deltoid muscle is easily accessible and has fewer nerve endings, making the injection less painful.
On the other hand, the biceps brachii is an important muscle in the upper arm involved in flexion of the forearm, and injecting a vaccine into this muscle could potentially interfere with its function and cause discomfort.