This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Which of the folowing is used to assess the communicability of a disease following the exposure to the primary case? 
Select and explain. 
A. Secondary attack rate, B. Generation time, C. Serial interval, D. Incubation period
A: Secondary attack rate
Answer: A: Secondary attack rate 
Explanation: Secondary attack rate is defined as the number of the exposed persons developing the disease within the range of the incubation period, following exposure to the primary cause. A measure of infectivity is the secondary attack rate. It reflects the degree of contagiousness of a communicable disease, and has been used in assessment of the effectiveness of control measures.