**Core Concept**
The term vaccine was coined by Edward Jenner, an English physician and scientist, who developed the first vaccine to prevent smallpox. This concept is rooted in the history of medicine, specifically the development of vaccines, which have revolutionized disease prevention.

**Why the Correct Answer is Right**
Edward Jenner introduced the term "vaccine" in 1796, derived from the Latin word "vacca," meaning cow. This was in reference to the cowpox virus, which he used to develop the first vaccine. Jenner's pioneering work led to the development of vaccines for other diseases, saving countless lives. The vaccine's mechanism of action involves stimulating the immune system to produce antibodies against specific pathogens, providing long-term immunity.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the term "vaccine" was not coined by Louis Pasteur, who made significant contributions to vaccination but did not introduce the term.
**Option B:** This option is incorrect because Robert Koch, a German physician, made significant contributions to microbiology but did not coin the term "vaccine."
**Option C:** This option is incorrect because Alexander Fleming, a Scottish biologist, discovered penicillin but did not introduce the term "vaccine."
**Option D:** This option is incorrect because this answer choice is missing.

**Clinical Pearl / High-Yield Fact**
Edward Jenner's development of the smallpox vaccine in 1796 marked the beginning of vaccine development, which has saved millions of lives worldwide. This milestone highlights the importance of vaccination in preventing infectious diseases.

**Correct Answer:** C.