WBR0039
| Author | PageAuthor::Gonzalo Romero |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biostatistics/ Epidemiology |
| Sub Category | SubCategory::Infectious Disease |
| Prompt | [[Prompt::A new vaccine is being developed to prevent the new strand of Influenza H7N9 or bird flu recently causing an outbreak in China. A Clinical Trial concludes that this vaccine could be used in the general population to prevent this “bird flu”; the vaccine is effective in developing an immune response. A Committee of practicing physicians in China is trying to understand the effect of such intervention in some epidemiologic measures. What would be the most appropriate statement of the following about this new vaccine's effect?]] |
| Answer A | AnswerA::Prevalence decreases and Incidence remains unchanged |
| Answer A Explanation | [[AnswerAExp::Incorrect. Prevalence could decrease if for example; the mortalitiy or recovery increases even though Incidence or new cases remain unchanged. This is not the case presented in the vignette]] |
| Answer B | AnswerB::Incidence decreases |
| Answer B Explanation | [[AnswerBExp::Correct. Correct due to the explained above]] |
| Answer C | AnswerC::Incidence will increase and concomitantly prevalence will increase |
| Answer C Explanation | [[AnswerCExp::Incorrect. This is not logical, because incidence decreases.]] |
| Answer D | AnswerD::No effect will be seen |
| Answer D Explanation | [[AnswerDExp::Incorrect. The vaccine was proved to be effective, so an effect will be seen]] |
| Answer E | AnswerE::Prevalence will decrease and Incidence will remain unchanged |
| Answer E Explanation | [[AnswerEExp::Incorrect. Prevalence depends also in Incidence, Mortality and Recovery. It makes sense in the case of chronic conditions that a decrease in incidence will reduce the prevalence. With this vaccination Incidence will decrease.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::This question is testing basic epidemiologic concepts. A vaccine for an acute condition will decrease the incidence or appearance of new cases. Prevalence = Incidence X Duration, therefore the Incidence equals Prevalence in the case of Acute cases such as Influenza.
If hypothetically Influenza would cause chronic cases, this will create a prevalente pot or poll. Creating a vaccine which decreases incidence will eventually decrease the prevalence. For example vaccination against Poliomyelitis decreases Incidence of acute polio, therefore the prevalence of Polio consequences.
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| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |