Virology: polio eradication: practice question

A Microbiology 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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Microbiology · Virology: polio eradication

Sample item

Since 2016 the trivalent oral polio vaccine was replaced by a bivalent vaccine containing types 1 and 3, with inactivated vaccine added to the routine schedule. What was the main reason for removing the type 2 component?

AType 2 virus has an animal reservoirBType 2 vaccine strain had low immunogenicityCType 2 vaccine was too expensiveDWild type 2 was eradicated and the vaccine type 2 strain was causing circulating vaccine-derived paralytic polio

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

The answer and the reasoning

D. Wild type 2 was eradicated and the vaccine type 2 strain was causing circulating vaccine-derived paralytic polio

Wild poliovirus type 2 was declared eradicated in 2015, yet the Sabin type 2 strain could revert and cause circulating vaccine-derived poliovirus outbreaks in under-immunised populations. Withdrawing it, with IPV to provide type 2 protection, removes this source. Polio has no animal reservoir, and the type 2 strain was in fact highly immunogenic.

Option by option

A. Type 2 virus has an animal reservoir
Poliovirus infects humans only and has no animal reservoir.
B. Type 2 vaccine strain had low immunogenicity
The type 2 strain was highly immunogenic, which is partly why it spread.
C. Type 2 vaccine was too expensive
Cost was not the reason for the switch.
D. Wild type 2 was eradicated and the vaccine type 2 strain was causing circulating vaccine-derived paralytic polio (correct)
Correct. Eradication of wild type 2 and reversion of the vaccine strain justified withdrawal.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Wild type 2 was eradicated and the vaccine type 2 strain was causing circulating vaccine-derived paralytic polio. Wild poliovirus type 2 was declared eradicated in 2015, yet the Sabin type 2 strain could revert and cause circulating vaccine-derived poliovirus outbreaks in under-immunised populations.

Why is "Type 2 virus has an animal reservoir" not the answer?

Poliovirus infects humans only and has no animal reservoir.

Why is "Type 2 vaccine strain had low immunogenicity" not the answer?

The type 2 strain was highly immunogenic, which is partly why it spread.

Why is "Type 2 vaccine was too expensive" not the answer?

Cost was not the reason for the switch.

What concept does this question test?

It tests Virology: polio eradication in Microbiology. Withdrawing it, with IPV to provide type 2 protection, removes this source. Polio has no animal reservoir, and the type 2 strain was in fact highly immunogenic.

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 Virology: polio eradication?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.