A ceain commuity has 100 children out of whom 28 are immunuzed against measles; 2 of them acquire measles simultaneously; Subsequently 14 get measles. Assuming the efficacy of vaccine to be 100%. What is the sec. Attack rate –
**Core Concept**
The question tests the understanding of **secondary attack rate**, a measure used in epidemiology to assess the spread of a disease within a population. It specifically looks at the incidence of a disease among the contacts of a primary case. **Vaccine efficacy** is also a key concept, referring to the ability of a vaccine to prevent disease under controlled conditions.
**Why the Correct Answer is Right**
Given that the vaccine is 100% effective, the 28 immunized children are not at risk of acquiring measles. Among the remaining 72 non-immunized children, 2 initially acquire measles, and then 14 more get infected. The secondary attack rate is calculated as the number of new cases among the susceptible population divided by the total number of susceptible individuals. Here, it would be the 14 new cases divided by the 70 susceptible individuals (72 non-immunized minus the 2 initial cases).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the calculation based on the provided numbers and the definition of secondary attack rate.
**Option B:** Similarly, this is incorrect as it does not align with the formula for calculating the secondary attack rate in the context given.
**Option D:** This option is also incorrect for the same reasons as options A and B.
**Clinical Pearl / High-Yield Fact**
Remember, the secondary attack rate is a crucial measure for understanding the contagiousness of a disease and the effectiveness of preventive measures like vaccination. In real-world scenarios, vaccine efficacy might not be 100%, affecting the calculation and interpretation of the secondary attack rate.
**Correct Answer:** C. 20%