## Core Concept
Measles elimination is a public health goal that aims to stop the endemic transmission of measles virus. It is defined based on the interruption of continuous, indigenous measles transmission within a defined geographic area. This concept is crucial in epidemiology and public health policy.

## Why the Correct Answer is Right
The correct answer, **D. Reduction of measles incidence to less than 1 per 100,000 population per year**, aligns with the World Health Organization's (WHO) definition of measles elimination. According to the WHO, a region or country is considered to have eliminated measles if it sustains a measles incidence of less than 1 case per 100,000 population per year over a period of at least 12 months, with high-quality surveillance to detect and confirm suspected cases.

## Why Each Wrong Option is Incorrect
- **Option A:** "Absence of measles for 10 years" - This option is incorrect because elimination does not require a complete absence of measles cases for 10 years but rather a sustained low incidence rate.
- **Option B:** "Reduction of measles incidence to less than 10 per 100,000 population per year" - This is incorrect because the threshold for elimination is specifically less than 1 case per 100,000 population per year, not 10.
- **Option C:** "Measles vaccination coverage of more than 80%" - While high vaccination coverage is crucial for achieving and maintaining measles elimination, the definition of elimination itself focuses on the incidence rate, not the vaccination coverage.

## Clinical Pearl / High-Yield Fact
A key point to remember is that measles elimination is not the same as eradication. Eradication implies the complete and permanent reduction of a disease to zero worldwide. Elimination refers to the reduction of disease incidence to an acceptable level within a specified geographic area. Achieving and maintaining elimination requires sustained efforts, including high vaccination coverage and strong surveillance systems.

**Correct Answer: D. Reduction of measles incidence to less than 1 per 100,000 population per year.**