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{{WBRQuestion | {{WBRQuestion | ||
|QuestionAuthor=Gonzalo Romero (Reviewed by Will Gibson and Yazan Daaboul) | |QuestionAuthor=Gonzalo Romero (Reviewed by Will Gibson and Yazan Daaboul) | ||
|ExamType=USMLE Step 1 | |ExamType=USMLE Step 1 | ||
|MainCategory=Biostatistics/ Epidemiology | |MainCategory=Biostatistics/Epidemiology | ||
|SubCategory=General Principles | |SubCategory=General Principles | ||
|Prompt=A new vaccine is being developed to prevent a new H7N9 strain of influenza that has recently caused an outbreak in China. A clinical trial concludes that this vaccine provides a relative risk reduction of 96% for influenza infection in the general population. A committee of practicing physicians in China is attempting to understand the potential epidemiological effect of this intervention . Which of the following will be the most appropriate statement regarding this new vaccine's effect? | |||
|Prompt=A new vaccine is being developed to prevent | |||
|Explanation=This question is testing basic epidemiologic concepts. [[Incidence]] is defined as the number of new cases within a given time period. [[Prevalence]] is the number of people affected by a given condition at a single point in time. The prompt stated that the vaccine will be 96% effective in preventing new cases. Therefore, the incidence will decrease. Because [[prevalence]] is equal to [[incidence]] multiplied by the average duration of disease, the prevalence of the disease will decrease as well. | |Explanation=This question is testing basic epidemiologic concepts. [[Incidence]] is defined as the number of new cases within a given time period. [[Prevalence]] is the number of people affected by a given condition at a single point in time. The prompt stated that the vaccine will be 96% effective in preventing new cases. Therefore, the incidence will decrease. Because [[prevalence]] is equal to [[incidence]] multiplied by the average duration of disease, the prevalence of the disease will decrease as well. | ||
[[Prevalence]] = [[Incidence]] x Average duration of disease | |||
|AnswerA=Prevalence will decrease and incidence will remain unchanged | |AnswerA=Prevalence will decrease and incidence will remain unchanged | ||
|AnswerAExp=[[Prevalence]] could decrease if for example; the average duration of disease increases even though [[incidence]] remains unchanged. There is no evidence in the prompt that the vaccine will cause people to recover less quickly from [[influenza]] infection. | |AnswerAExp=[[Prevalence]] could decrease if for example; the average duration of disease increases even though [[incidence]] remains unchanged. There is no evidence in the prompt that the vaccine will cause people to recover less quickly from [[influenza]] infection. | ||
|AnswerB= | |AnswerB=Both incidence and prevalence will decrease | ||
|AnswerBExp=The prompt states that the vaccine will be 96% effective in preventing new cases of [[influenza]]. Because the incidence represents the rate of new cases, the [[vaccine]] will decrease the incidence. | |AnswerBExp=The prompt states that the vaccine will be 96% effective in preventing new cases of [[influenza]]. Because the incidence represents the rate of new cases, the [[vaccine]] will decrease the incidence. Prevalence is proportional to the incidence. Accordingly, prevalence will also decrease. | ||
|AnswerC= | |AnswerC=Both incidence and prevalence will increase | ||
|AnswerCExp=Because the [[vaccine]] will decrease the [[incidence]] of the disease, the [[prevalence]] will also decrease. | |AnswerCExp=Because the [[vaccine]] will decrease the [[incidence]] of the disease, the [[prevalence]] will also decrease. | ||
|AnswerD=No effect on either prevalence or incidence will be | |AnswerD=No effect on either prevalence or incidence will be observed | ||
|AnswerDExp=[[Incidence]] is an epidemiologic measure representing the number of new cases in a given time period. | |AnswerDExp=[[Incidence]] is an epidemiologic measure representing the number of new cases in a given time period. Because the [[vaccine]] is shown to be 96% effective in preventing new cases of [[influenza]], the [[incidence]] is expected to decrease. Because [[incidence]] is proportional to prevalence, prevalence will also decrease. | ||
|AnswerE=Prevalence will decrease and incidence will remain unchanged | |AnswerE=Prevalence will decrease and incidence will remain unchanged | ||
|AnswerEExp=[[Prevalence]] depends on incidence and the average duration of disease. Prevalence will be much greater than incidence with chronic conditions where the average duration of disease is long. With short-lived conditions, such as [[influenza]], the incidence will closely reflect the [[prevalence]]. Therefore, it is expected that the [[vaccine]] | |AnswerEExp=[[Prevalence]] depends on incidence and the average duration of disease. Prevalence will be much greater than incidence with chronic conditions where the average duration of disease is long. With short-lived conditions, such as [[influenza]], the incidence will closely reflect the [[prevalence]]. Therefore, it is expected that the [[vaccine]] will decrease both the [[prevalence]] and [[incidence]] of this strain of [[influenza]]. | ||
|EducationalObjectives=[[Prevalence]] is defined as the number of current cases of a particular disease. [[Incidence]] is defined as the number of new cases of a particular disease in a given time period. The relationship between [[prevalence]] and [[incidence]] can be summarized in the equation below: | |EducationalObjectives=[[Prevalence]] is defined as the number of current cases of a particular disease. [[Incidence]] is defined as the number of new cases of a particular disease in a given time period. The relationship between [[prevalence]] and [[incidence]] can be summarized in the equation below: | ||
[[Prevalence]] = [[Incidence]] x | [[Prevalence]] = [[Incidence]] x Average duration of disease | ||
|References=First Aid 2014 page 52 | |References=First Aid 2014 page 52 | ||
|RightAnswer=B | |RightAnswer=B | ||
|WBRKeyword= | |WBRKeyword=Biostatistics, Epidemiology, Incidence, Prevalence, Vaccine, Risk | ||
|Approved=Yes | |Approved=Yes | ||
}} | }} | ||
Latest revision as of 23:08, 27 October 2020
| Author | PageAuthor::Gonzalo Romero (Reviewed by Will Gibson and Yazan Daaboul) |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biostatistics/Epidemiology |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A new vaccine is being developed to prevent a new H7N9 strain of influenza that has recently caused an outbreak in China. A clinical trial concludes that this vaccine provides a relative risk reduction of 96% for influenza infection in the general population. A committee of practicing physicians in China is attempting to understand the potential epidemiological effect of this intervention . Which of the following will be the most appropriate statement regarding this new vaccine's effect?]] |
| Answer A | AnswerA::Prevalence will decrease and incidence will remain unchanged |
| Answer A Explanation | [[AnswerAExp::Prevalence could decrease if for example; the average duration of disease increases even though incidence remains unchanged. There is no evidence in the prompt that the vaccine will cause people to recover less quickly from influenza infection.]] |
| Answer B | AnswerB::Both incidence and prevalence will decrease |
| Answer B Explanation | [[AnswerBExp::The prompt states that the vaccine will be 96% effective in preventing new cases of influenza. Because the incidence represents the rate of new cases, the vaccine will decrease the incidence. Prevalence is proportional to the incidence. Accordingly, prevalence will also decrease.]] |
| Answer C | AnswerC::Both incidence and prevalence will increase |
| Answer C Explanation | [[AnswerCExp::Because the vaccine will decrease the incidence of the disease, the prevalence will also decrease.]] |
| Answer D | AnswerD::No effect on either prevalence or incidence will be observed |
| Answer D Explanation | [[AnswerDExp::Incidence is an epidemiologic measure representing the number of new cases in a given time period. Because the vaccine is shown to be 96% effective in preventing new cases of influenza, the incidence is expected to decrease. Because incidence is proportional to prevalence, prevalence will also decrease.]] |
| Answer E | AnswerE::Prevalence will decrease and incidence will remain unchanged |
| Answer E Explanation | [[AnswerEExp::Prevalence depends on incidence and the average duration of disease. Prevalence will be much greater than incidence with chronic conditions where the average duration of disease is long. With short-lived conditions, such as influenza, the incidence will closely reflect the prevalence. Therefore, it is expected that the vaccine will decrease both the prevalence and incidence of this strain of influenza.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::This question is testing basic epidemiologic concepts. Incidence is defined as the number of new cases within a given time period. Prevalence is the number of people affected by a given condition at a single point in time. The prompt stated that the vaccine will be 96% effective in preventing new cases. Therefore, the incidence will decrease. Because prevalence is equal to incidence multiplied by the average duration of disease, the prevalence of the disease will decrease as well.
Prevalence = Incidence x Average duration of disease Prevalence = Incidence x Average duration of disease |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Biostatistics, WBRKeyword::Epidemiology, WBRKeyword::Incidence, WBRKeyword::Prevalence, WBRKeyword::Vaccine, WBRKeyword::Risk |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |