A herd immunity of over – % is considered necessary to prevent epidemic spread of diphtheria –
**Core Concept**
The concept of herd immunity is crucial in preventing the spread of infectious diseases, including diphtheria. Herd immunity refers to the proportion of the population that needs to be immune to a disease to prevent its spread. This concept is based on the principle of **epidemiology** and **immunology**.
**Why the Correct Answer is Right**
To determine the correct answer, we need to consider the **basic reproduction number** of diphtheria, which is estimated to be around 2-3. However, the exact herd immunity threshold for diphtheria is not explicitly stated in the question. Generally, for diseases with a basic reproduction number of 2-3, a herd immunity threshold of 80-90% is considered necessary to prevent epidemic spread.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a lower percentage would not provide sufficient immunity to prevent the spread of diphtheria.
**Option B:** This option may be incorrect because it might be too low to achieve herd immunity for diphtheria.
**Option D:** This option is incorrect because a higher percentage than necessary would not provide additional benefits in preventing the spread of diphtheria.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the herd immunity threshold varies depending on the **basic reproduction number** of the disease. For highly contagious diseases like measles, a higher threshold of 93-95% is required.
**Correct Answer:** D. 85% is generally considered the threshold for diphtheria, but since the answer is not provided, the general threshold for many infectious diseases like diphtheria is around 85%, thus **Correct Answer: D. 85%.**