**Core Concept**
Mass immunization is a public health strategy used to control and prevent the spread of infectious diseases by vaccinating a large proportion of the population. This approach is particularly effective against highly contagious diseases with significant morbidity and mortality.

**Why the Correct Answer is Right**
Mass immunization is indicated in situations where the disease is highly transmissible, has a high case-fatality rate, or has a significant impact on public health. For example, in the case of measles, mass immunization has been instrumental in reducing the number of cases and deaths worldwide. The measles vaccine induces immunity by stimulating the production of antibodies against the measles virus, thereby preventing the disease from spreading.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** This option is not provided.
**Option C:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
It's essential to note that mass immunization is not always 100% effective, and some individuals may still develop the disease despite being vaccinated. However, the benefits of mass immunization far outweigh the risks, and it remains a crucial tool in controlling infectious disease outbreaks.

**Correct Answer:** A.