**Core Concept**
The measles vaccine is a live attenuated vaccine that provides immunity against measles, a highly contagious viral infection. The vaccine's efficiency is crucial in preventing outbreaks and controlling the spread of the disease.

**Why the Correct Answer is Right**
The measles vaccine's efficiency is attributed to its ability to induce both humoral and cellular immunity. The vaccine virus replicates in the body, stimulating the production of antibodies and activating T-cells, which provide long-term protection against the disease. The vaccine's efficiency is also influenced by factors such as the number of vaccine doses administered, the timing of the doses, and the presence of underlying health conditions.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide any information about the measles vaccine's efficiency.
**Option B:** This option is incorrect because it suggests that the measles vaccine's efficiency is solely dependent on the presence of underlying health conditions, which is not the case.
**Option C:** This option is incorrect because it implies that the measles vaccine's efficiency is only effective for a short period of time, which is not true.

**Clinical Pearl / High-Yield Fact**
The measles vaccine is generally considered to be 93% effective in preventing measles in individuals who receive two doses of the vaccine, with a single dose being about 85% effective.

**Correct Answer: D.**