**Core Concept**
Herd immunity refers to a situation where a significant portion of a population becomes immune to a disease, thereby protecting susceptible individuals who are not immune. This concept is crucial in preventing the spread of infectious diseases and has significant implications for public health.

**Why the Correct Answer is Right**
The correct answer, option B, is incorrect because herd immunity is actually less likely for infections that do not have a subclinical phase. Infections with a subclinical phase can spread undetected, allowing the pathogen to circulate in the population and increasing the likelihood of herd immunity. In contrast, infections without a subclinical phase, such as some viral hemorrhagic fevers, can spread rapidly among individuals who are not immune, but the lack of a subclinical phase actually makes herd immunity less effective because the disease spreads more quickly.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true and is a fundamental aspect of herd immunity. The protection afforded by immunized individuals not only protects them but also indirectly protects the susceptible individuals within the population.

**Option C:** This statement is true and highlights the importance of considering alternative animal hosts in the transmission and spread of infectious diseases. The presence and distribution of alternative animal hosts can impact the effectiveness of herd immunity by influencing the transmission dynamics of the disease.

**Option D:** This statement is true and specifically addresses the concept of herd immunity in the context of tetanus. Tetanus is a highly infectious disease, but it does not spread from person to person. Therefore, herd immunity does not protect the individual against tetanus infection.

**Clinical Pearl / High-Yield Fact**
When considering herd immunity, it is essential to remember that the effectiveness of this concept depends on the presence of a subclinical phase in the disease. Infections with a subclinical phase are more likely to achieve herd immunity, whereas those without a subclinical phase may not be as effective in achieving this goal.

**Correct Answer Line**
✓ Correct Answer: B. It is likely to be more for infections that do not have a sub-clinical phase.