This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
[{'content': 'What is the period of infectivity in measles? \nSelect and explain. \nA. From 7 days to 7 days after the rash, B. From 4 days to 4 days after the rash, C. From 9 days to 12 days after the rash, D. From 5 days to 9 days after the rash', 'role': 'user'}, {'content': 'Answer: B \nExplanation: <p>MEASLES:- An acute highly infectious disease of childhood caused by a specific virus of group myxovirus. Clinically characterised by fever and catarrhal symptoms of the upper respiratory tract( coryza,cough), followed by a typical rash. When the disease is introduced into a virgin community,more than 90% of population will be affected. Communicability- 4 days before the appearance of rash to 4 days after. Incubation period-10 days from exposure to onset of fever and 14 days of appearance of rash. Secondary attack rate-infection confers life long immunity as there is only one antigenic type. Vaccine- live attenuated subcutaneous vaccine. {Reference: park&;s textbook of preventive and social medicine, 23rd edition, pg no.149}</p>', 'role': 'assistant'}]