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
[{'content': 'Smallpox eradication was successful due to all of the following reasons except \nSelect and explain. \nA. Subclinical cases did not transmit the disease, B. A highly effective vaccine was available, C. Cross-resistance existed with animal pox, D. Infection provided lifelong immunity', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Epidemiological Reasons/Basis For Smallpox Eradication:\n• No known animal reservoir\n• No long term carrier state\n• Infection provides lifelong immunity\n• Case detection simple due to characteristic rash\n• Subclinical cases did not transmit the disease\n• A highly effective vaccine was available\n• International cooperation', 'role': 'assistant'}]