Measles outbreak response — DTM&H MCQ

Correct answer: E — Non-selective mass vaccination for all children 6 months to 15 years

The correct answer is E: non-selective mass vaccination for all children 6 months to 15 years. With only 40 percent vaccination coverage in a population of 30,000, the immunity gap is far below the herd immunity threshold required for measles (which needs greater than 95 percent coverage given its very high transmissibility), so a rapid, non-selective campaign is needed rather than one reliant on checking individual vaccination histories, which delays response. Sphere and MSF humanitarian standards specify that outbreak response immunisation in camp settings should target all children aged 6 months to under 15 years regardless of prior vaccination status, because older children in camps are frequent efficient spreaders and case fatality remains significant up to adolescence in crowded, malnourished populations. Non-selective delivery is logistically faster and avoids the errors and delays of history-taking during an active outbreak, maximising population coverage before further transmission occurs. Why the other options are wrong: C. Targeted vaccination of unvaccinated under-5s only: this ignores the substantial proportion of cases and transmission occurring in the 5 to 15 year age group in camp outbreaks, and verifying vaccination status individually is slow and unreliable during an emergency. A. Post-exposure immunoglobulin for all contacts: immunoglobulin is reserved for specific high-risk individuals (for example immunocompromised or pregnant contacts) exposed within a narrow window, not a scalable mass outbreak control tool for 30,000 people. D. Isolation with no vaccination: isolation alone cannot control spread given measles' extremely high basic reproduction number and pre-symptomatic infectiousness, and does nothing to close the underlying immunity gap. B. Mass vitamin A alone: vitamin A reduces measles-associated morbidity and mortality and should accompany vaccination, but it has no effect on transmission and is not a substitute for immunisation. Key point: In a measles outbreak with low background immunity in a humanitarian camp setting, rapid non-selective vaccination of all children 6 months to under 15 years (irrespective of vaccination status) is the standard outbreak control strategy, with vitamin A given alongside, not instead of, vaccine.

Reference: MSF Medical Guidelines, 4.4 Choosing the outbreak response vaccination strategy: non-selective vaccination targeting children 6 months to under 15 years is the preferred outbreak response strategy in humanitarian emergencies (Sphere Project standard), https://medicalguidelines.msf.org/en/viewport/mme/english/4-4-choosing-the-outbreak-response-vaccination-strategy-32407930.html