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
Small pox eradication was successful because of all except- 
Select and explain. 
A. Subclinical cases don't transmit disease, B. Highly effective vaccine -, C. Lifelong immunity, D. Cross resistance with animal pox
D: Cross resistance with animal pox
Answer: D: Cross resistance with animal pox 
Explanation: None