Correct Answer: Inoculate

Solution : The correct choice is the second option.

Explanation : The phrase "treat with a vaccine, usually by injection to promote immunity against a disease", describes a medical procedure related to introducing a vaccine into the body. The term that precisely conveys this meaning is inoculate, which refers to the action of treating a person or animal with a vaccine to produce immunity against a particular disease.

The meanings of the other options are as follows:

• Innuendo : This word refers to an indirect or subtle suggestion or hint, typically with a negative connotation.
• Innumerate : This word means lacking numerical skills or being unable to understand or use numbers.
• Innovate : This word means to introduce something new or make changes in existing methods or processes.

Therefore, the right answer is inoculate .