To eradicate measles the percentage of population to be caccinated is at least ______% –
## Core Concept
The concept being tested here revolves around the **herd immunity threshold** required to eradicate infectious diseases, specifically measles. Eradication of a disease such as measles requires a high enough vaccination rate to prevent sustained transmission. The **basic reproduction number (R0)**, which represents the number of secondary cases generated by a single infected individual in a fully susceptible population, is crucial. For measles, R0 is estimated to be around 12-18.
## Why the Correct Answer is Right
The correct answer, **95%**, is based on the high contagiousness of measles, reflected in its high R0. To achieve herd immunity and prevent outbreaks, the vaccination coverage must exceed the threshold where R0 equals 1, adjusted for the vaccine's effectiveness. For measles, with a highly effective vaccine (around 93% effective with one dose and 97% with two doses), a coverage of at least **95%** is generally recommended to ensure herd immunity and facilitate the potential for eradication. This threshold helps protect those who are not vaccinated, such as individuals with certain medical conditions.
## Why Each Wrong Option is Incorrect
- **Option A (80%):** This is too low for measles due to its high R0. At 80%, the population would remain vulnerable to outbreaks.
- **Option B (85%):** Still insufficient for measles. This level of coverage might be adequate for diseases with lower R0 values but not for measles.
- **Option D (90%):** While closer, it does not provide the necessary herd immunity threshold for measles, given its contagiousness and the vaccine's effectiveness.
## Clinical Pearl / High-Yield Fact
A key point to remember is that **measles requires a very high vaccination rate** to prevent outbreaks and move towards eradication. The vaccine is highly effective, but two doses are often needed to achieve optimal protection, highlighting the importance of not just the percentage of the population vaccinated but also the completeness of vaccination (i.e., one vs. two doses).
## Correct Answer: C. 95%