Communicable diseases: vaccine-derived poliovirus: 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 · Communicable diseases: vaccine-derived poliovirus

Sample item

In a district with poor routine immunisation coverage, a child with acute flaccid paralysis has a poliovirus isolated from stool that is genetically diverged from the Sabin type 2 vaccine strain. Wild poliovirus type 2 has been eradicated globally. What is the most likely explanation?

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

The answer and the reasoning

A. Prolonged replication of vaccine virus in an under-immunised community with reversion to neurovirulence

Live oral vaccine virus can circulate for long periods in populations with low immunity, accumulating mutations and regaining neurovirulence, which gives a circulating vaccine-derived poliovirus. This is the reason for withdrawing type 2 from the oral vaccine and using inactivated vaccine, along with raising routine coverage.

Option by option

  • A. Prolonged replication of vaccine virus in an under-immunised community with reversion to neurovirulence (correct)

    Correct. Extended person-to-person spread of the attenuated vaccine strain in a poorly immunised community can restore paralytic potential.

  • B. Contamination of inactivated polio vaccine with live virus

    Inactivated polio vaccine contains killed virus and cannot cause infection.

  • C. Spontaneous mutation of wild poliovirus type 1 into type 2

    Wild type 1 does not change into type 2 virus, which is a distinct serotype.

  • D. Reactivation of a latent poliovirus infection acquired earlier

    Poliovirus does not establish latency and cannot reactivate.

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.

More PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is A, Prolonged replication of vaccine virus in an under-immunised community with reversion to neurovirulence. Live oral vaccine virus can circulate for long periods in populations with low immunity, accumulating mutations and regaining neurovirulence, which gives a circulating vaccine-derived poliovirus.

Why is "Contamination of inactivated polio vaccine with live virus" not the answer?

Inactivated polio vaccine contains killed virus and cannot cause infection.

Why is "Spontaneous mutation of wild poliovirus type 1 into type 2" not the answer?

Wild type 1 does not change into type 2 virus, which is a distinct serotype.

Why is "Reactivation of a latent poliovirus infection acquired earlier" not the answer?

Poliovirus does not establish latency and cannot reactivate.

What concept does this question test?

It tests Communicable diseases: vaccine-derived poliovirus in PSM. This is the reason for withdrawing type 2 from the oral vaccine and using inactivated vaccine, along with raising routine coverage.

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 Communicable diseases: vaccine-derived poliovirus?

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.