**Core Concept:**
Herd immunity is a phenomenon in which vaccination of a significant proportion of a population (herd) protects those who cannot be vaccinated, such as babies, immunocompromised individuals, and pregnant women, from infectious diseases. Mass vaccination refers to immunizing a large proportion of a population simultaneously, which is one strategy to achieve herd immunity.

**Why the Correct Answer is Right:**
Mass vaccination aims to protect vulnerable groups by reducing the spread of infectious diseases in the community. Vaccines work by stimulating the immune system to produce immunity without causing the actual disease. Herd immunity is achieved when a significant proportion of the population (usually 70-90%) is immune to a pathogen, either through vaccination or previous infection.

**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because herd immunity can be achieved through vaccination of a significant proportion of the population. While herd immunity does not depend on individual vaccination rates, focusing solely on individual immunization may not be sufficient to protect vulnerable groups.

B. This option is incorrect because the aim of mass vaccination is to reduce disease transmission in the community, leading to herd immunity. Vaccination of a significant proportion of the population is essential for this purpose.

C. This option is incorrect because herd immunity is achieved through vaccination or previous infection of a significant proportion of the population. Achieving herd immunity through only isolating infected individuals is not a practical solution in a large population and may not protect vulnerable groups effectively.

D. This option is incorrect because herd immunity can be achieved through vaccination of a significant proportion of the population. Targeting a specific group does not guarantee protection for vulnerable individuals when the pathogen can still spread within the larger community.

**Clinical Pearl:**
Mass vaccination campaigns should focus on vaccinating a large portion of the population to effectively protect vulnerable groups and reduce the spread of infectious diseases in the community. Targeting specific groups alone may not achieve herd immunity and protect those who cannot be vaccinated.