Disease eradication: feasibility: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Disease eradication: feasibility

Sample item

Smallpox was eradicated but poliomyelitis has proved much harder to eradicate. Which feature of poliovirus infection most directly explains this difference?

AInfection does not induce immunityBOnly a single serotype exists and the vaccine is ineffectiveCMost infections are subclinical yet infectious, so cases cannot be found easilyDThe virus has an extensive animal reservoir

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Most infections are subclinical yet infectious, so cases cannot be found easily

Smallpox produced visible disease in nearly all infected people, so surveillance and ring vaccination could find every chain of transmission. In polio about 95 percent or more of infections are inapparent, yet these people shed virus, so many transmission chains stay hidden. Humans are the only reservoir of poliovirus, and vaccines are effective.

Option by option

A. Infection does not induce immunity
Natural infection and vaccination do induce type-specific immunity.
B. Only a single serotype exists and the vaccine is ineffective
There are three serotypes, and vaccines are highly effective, so this statement is false.
C. Most infections are subclinical yet infectious, so cases cannot be found easily (correct)
Correct. A large pool of asymptomatic excretors hides transmission and complicates surveillance.
D. The virus has an extensive animal reservoir
Poliovirus has no animal reservoir, and so reservoirs do not explain the difficulty.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, Most infections are subclinical yet infectious, so cases cannot be found easily. Smallpox produced visible disease in nearly all infected people, so surveillance and ring vaccination could find every chain of transmission.

Why is "Infection does not induce immunity" not the answer?

Natural infection and vaccination do induce type-specific immunity.

Why is "Only a single serotype exists and the vaccine is ineffective" not the answer?

There are three serotypes, and vaccines are highly effective, so this statement is false.

Why is "The virus has an extensive animal reservoir" not the answer?

Poliovirus has no animal reservoir, and so reservoirs do not explain the difficulty.

What concept does this question test?

It tests Disease eradication: feasibility in PSM. In polio about 95 percent or more of infections are inapparent, yet these people shed virus, so many transmission chains stay hidden. Humans are the only reservoir of poliovirus, and vaccines are effective.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Disease eradication: feasibility?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.