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': 'The protective value of vaccine is 95%. It means \nSelect and explain. \nA. All those vaccinated are protected, B. 5 among 100 have the probability of getting infected after vaccination, C. Among those vaccinated, 95% persons are not susceptible to the injections, D. 95% of persons do not get the disease, where as 5% get the disease', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Vaccine is an immuno-biological substance designed to produce specific protection against a given disease\nIt stimulates the production of protective antibody and other immune mechanisms\nVaccines can be prepared from live modified organisms, inactivated or killed organisms, extracted cellular fractions, toxoids or combination of these\nVaccine efficacy\xa0is the percentage reduction of disease in a vaccinated group of people compared to an unvaccinated group, using the most favorable conditions\nVaccine efficacy was designed and calculated by Greenwood and Yule in 1915 for cholera and typhoid\xa0vaccines\nIt is best measured using\xa0double-blind, randomized, clinical controlled trials, such that it is studied under “best case scenarios', 'role': 'assistant'}]