Measles in a Displacement Settlement: A Coverage Figure That Does Not Add Up
A settlement of 14,000 displaced people, 30% of them children under five. At entry screening, measles-containing vaccine first-dose coverage among children was recorded as 62%. A campaign 18 months ago reported 78% coverage of children aged 9 months to 5 years by administrative tally. In the past three weeks, 96 suspected measles cases have been reported in children under ten, with six deaths. Forty-one of the 96 have a documented measles vaccination, 55 have none. There is one primary health care centre with a cold chain that failed twice last month and a mobile team that visits twice weekly. Neighbouring host villages report 12 cases in the same period. National policy requires outbreak response immunisation within 15 days of laboratory confirmation; laboratory results take five days. The settlement manager wants the school closed today.
1. Write the case definition you would use and set out your first 72 hours, including how you confirm the outbreak. How do you interpret the finding that 41 of 96 cases were vaccinated?
Read the worked answer
Case definition. Suspected: any person in the settlement or neighbouring host villages with fever and generalised maculopapular rash, plus cough, coryza or conjunctivitis, with onset on or after the date the first case was notified. Confirmed: laboratory confirmation (measles IgM, or measles RNA on throat or nasopharyngeal swab or urine) or epidemiological linkage to a confirmed case. Keep suspected, confirmed and discarded categories in the line list.
First 72 hours. Activate the line list and active case finding at the health centre, schools, churches and mosques, and by house-to-house search; build the epidemic curve by date of rash onset and map cases; collect specimens from the first 5–10 cases, ideally within 3 days of rash onset and no later than 28 days; begin immediate planning for outbreak response immunisation rather than waiting for the laboratory. Notify the national programme and coordinate with the host-village authorities, since the 12 cases there show this is not contained.
The 6.3% case fatality (6/96) is high and suggests under-ascertainment of mild cases, delayed care, malnutrition and vitamin A deficiency. Treat it as a signal to strengthen case finding and clinical management, not as a reason to doubt the diagnosis.
The 41 vaccinated cases. This is expected and does not discredit the vaccine. One dose protects roughly 85% of recipients; two doses about 97%. Some of the 41 may have received a single dose, some may have been vaccinated within 14 days of exposure (too late to protect), and some records may be inaccurate. With low coverage, most cases will still occur among the vaccinated simply because the vaccinated are the majority - compute attack rates by vaccination status once denominators are available.
2. Design the outbreak response. Address whether to wait for laboratory results, the target age range, the cold chain problem, vitamin A and what to do about the school.
Read the worked answer
Do not wait. The 15-day rule is a ceiling, not a target. With a compatible clinical picture, an epidemic curve, six deaths and a neighbouring area affected, the balance of harm favours starting now. Five days of laboratory time plus procurement and mobilisation would consume most of the window. Pre-position vaccine and begin community mobilisation immediately; adjust only if the laboratory discards the outbreak.
Target population. Children from 6 months to 10 years in the settlement and host villages, with a second dose for those who already have one documented dose and catch-up for the 9 months to 5 years cohort assumed covered by the campaign. Include health workers. Giving a dose at 6–8 months is acceptable in outbreaks, but those children need a further dose at 9 months and the schedule must record that.
Cold chain. Do not launch with a failed cold chain - heat-damaged vaccine gives false reassurance and wastes the campaign. Use cold boxes with conditioned ice packs, vaccine vial monitors, twice-daily temperature logs, and a named cold chain officer. The mobile team's twice-weekly schedule is too slow for outbreak response; add fixed daily posts plus house-to-house teams.
Vitamin A. Two doses 24 hours apart for every child with measles, and for all children with malnutrition in the affected area. Manage complications: oral rehydration, antibiotics for pneumonia and ear infection, eye care, nutritional support, referral criteria.
School. Closure is popular but weak here: transmission is community-wide, not school-specific. Prioritise vaccinating and excluding cases from school for four days after rash onset. A short closure can be considered if the school is demonstrably the main mixing site, but it must not substitute for immunisation.
3. After the outbreak, what would you conclude about the 78% administrative coverage figure, and what changes would you make to the programme's monitoring?
Read the worked answer
What 78% actually means. Administrative coverage is doses delivered divided by an estimated target population. Both terms are unreliable in displacement settings: denominators shift with arrivals, departures and age-structure assumptions, and doses given by mobile teams or private providers may never be recorded. Even taken at face value, 78% is far below the roughly 95% two-dose coverage needed to stop measles transmission. Worse, national averages hide heterogeneity - an overall 78% can coexist with settlements at 40%, and measles finds those pockets first. Cold chain failures in the last month reduce effective coverage further: a dose recorded as given through a compromised chain may be immunologically worthless.
Programme changes.
- Replace single administrative figures with a coverage survey using two-stage cluster sampling and card-plus-recall verification, and repeat it after every campaign.
- Report coverage by settlement and age cohort, not only as a district average, and map defaulters.
- Track two-dose completion and dropout between MCV1 and MCV2, not first dose alone.
- Make cold chain a monitored indicator: temperature logs audited weekly, vaccine vial monitor checks, functioning refrigerator count, and a named accountable officer.
- Strengthen case-based surveillance with laboratory confirmation and a zero-reporting requirement from the health centre and mobile teams.
- Review the immunity gap in older children who were outside the campaign age band.
- Pre-position an outbreak response stock and a pre-agreed trigger threshold so that the next response does not spend its first week negotiating supply.