Immunisation: Hib vaccine and herd effect: practice question

A Pediatrics 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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Pediatrics · Immunisation: Hib vaccine and herd effect

Sample item

After Haemophilus influenzae type b conjugate vaccine was introduced, invasive disease also fell among unimmunised young children in the community. What mechanism explains this?

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

The answer and the reasoning

A. Reduced nasopharyngeal carriage of the organism in vaccinated children

Conjugate vaccines induce mucosal immunity that lowers nasopharyngeal colonisation, so the organism circulates less and unvaccinated children are exposed less. This indirect effect is herd protection. Polysaccharide vaccines lack this effect on carriage.

Option by option

  • A. Reduced nasopharyngeal carriage of the organism in vaccinated children (correct)

    Correct. Lower carriage in the vaccinated reduces transmission to others.

  • B. Direct transfer of vaccine antibodies through breast milk

    Antibodies in breast milk do not explain community-level decline.

  • C. Rise in natural infection that boosted immunity

    Disease fell; natural infection did not rise.

  • D. Cross-protection from the vaccine against other bacterial species

    The vaccine protects against type b capsule only, not other species.

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.

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Questions about this Pediatrics question

What is the answer to this Pediatrics question?

The best answer is A, Reduced nasopharyngeal carriage of the organism in vaccinated children. Conjugate vaccines induce mucosal immunity that lowers nasopharyngeal colonisation, so the organism circulates less and unvaccinated children are exposed less.

Why is "Direct transfer of vaccine antibodies through breast milk" not the answer?

Antibodies in breast milk do not explain community-level decline.

Why is "Rise in natural infection that boosted immunity" not the answer?

Disease fell; natural infection did not rise.

Why is "Cross-protection from the vaccine against other bacterial species" not the answer?

The vaccine protects against type b capsule only, not other species.

What concept does this question test?

It tests Immunisation: Hib vaccine and herd effect in Pediatrics. This indirect effect is herd protection. Polysaccharide vaccines lack this effect on carriage.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Immunisation: Hib vaccine and herd effect?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.