**Question:** Vaccine which is eradicated worldwide is -

A. Smallpox
B. Polio
C. Measles
D. Rubella

**Core Concept:** Eradication of a disease refers to the global reduction of its incidence to zero through concerted public health efforts, including vaccination programs.

**Why the Correct Answer is Right:** Smallpox (Variola virus) was the first and only disease to be eradicated worldwide, achieved through the combined efforts of the World Health Organization (WHO) and vaccination campaigns. The smallpox vaccine, developed by Edward Jenner in the late 18th century, played a crucial role in its eradication.

**Why Each Wrong Option is Incorrect:**

A. Polio (Influenza virus) is incorrect because despite significant global efforts, polio remains endemic in certain regions, preventing its eradication.

B. Rubella (Rubella virus) is incorrect because while vaccination programs have reduced the incidence of rubella, eradication has not been achieved due to ongoing transmission in some parts of the world.

C. Measles (Measles virus) is incorrect because despite vaccination efforts, measles remains endemic in many regions.

**Why the Correct Answer is Right:** Smallpox eradication demonstrates the effectiveness of vaccination programs and global collaboration in combating infectious diseases and achieving significant public health goals.

**Clinical Pearl:** The success of smallpox eradication serves as an example for other infectious diseases, encouraging continued efforts to control and eliminate various global health challenges through vaccination campaigns and international collaboration.

**Correct Answer:** A. Smallpox