Uganda Study Evaluates Measles Outbreak Dynamics in Refugee Hosting District

A field investigation of a protracted measles outbreak in western Uganda has documented how localized gaps in routine two-dose immunization coverage and crowded indoor social gatherings sustained viral transmission across a vulnerable, refugee-hosting district. In June 2025, public health authorities were notified of suspected measles activity in Kamwenge District following serological confirmation of measles-specific immunoglobulin M antibodies in three pediatric patients. Subsequent active case finding and records reviews determined that transmission had been occurring across multiple subcounties since February 2025, ultimately identifying 109 cases comprising three laboratory-confirmed and 106 clinically compatible suspected cases. The epidemiological investigation, led by public health researchers and field epidemiology fellows, sought to quantify the outbreak’s magnitude, delineate key behavioral and environmental risk factors, and calculate field vaccine effectiveness alongside empirical coverage estimates among eligible community members.

Kamwenge District hosts a total population of 337,167 individuals across 17 subcounties, including an estimated 39,929 refugees residing largely within the Rwamwanja Refugee Settlement. The district has a documented history of recurrent measles episodes, including an outbreak recorded in March 2024. Across the February to July 2025 period examined by investigators, the overall attack rate across the district was determined to be 3.2 cases per 10,000 population. However, the disease burden was distributed unequally among demographic subgroups and geographic localities. Females exhibited an attack rate of 3.3 per 10,000, and children aged 9 to 17 months experienced the highest age-specific attack rate at 30.8 per 10,000, followed by children aged 18 to 59 months at 7.7 per 10,000. Furthermore, refugee residents experienced an attack rate of 13.3 per 10,000, which was substantially higher than the attack rate of 1.9 per 10,000 recorded among national residents.

Surveillance data revealed that 48.6 percent of the identified case-patients were refugees, and no fatalities occurred throughout the recorded event, with 79 percent of the 109 patients documented as fully recovered. Geographically, the highest subcounty-level attack rates clustered in areas hosting large refugee populations, specifically Nkoma-Katalyeba Town Council with an attack rate of 12 per 10,000 and Biguli Subcounty with an attack rate of 8 per 10,000. All identified case-patients presented with fever and generalized maculopapular rash, meeting the standardized clinical suspected case definition. Among these individuals, 80 percent developed cough, 69 percent experienced coryza, and 50 percent had conjunctivitis. Epidemiological curve mapping based on the date of rash onset indicated that transmission stretched over a multi-month period, demonstrating that cases detected in the April to July window represented an ongoing continuation of transmission established earlier in the year rather than an isolated introduction.

To investigate transmission pathways, the team initiated qualitative environmental assessments in selected health centers and community locations. At Rwamwanja Health Center IV in Nkoma-Katalyeba and Biguli Health Center III in Biguli Subcounty, assessments conducted by a single assessor noted operational vulnerabilities in infection prevention and control. Observed deficiencies included the management of suspected measles cases alongside other pediatric patients, a lack of dedicated or functional isolation infrastructure, and inadequate triage protocols. In community settings, assessments highlighted frequent attendance at crowded religious worship gatherings, particularly within Nkoma-Katalyeba Town Council, combined with limited community awareness regarding viral transmission mechanisms. Initial hypothesis-generation interviews with caregivers of case-patients identified frequent attendance at social gatherings in 79 percent of respondents, congregation at places of worship in 66 percent, school attendance in 53 percent, lack of vaccination in 46 percent, visits to water collection points in 39 percent, and playing away from home in 32 percent.

These preliminary signals were evaluated through a formal age-matched case-control study using neighborhood controls. Investigators enrolled 73 traced case-patients and 167 neighborhood controls across four age strata: under 9 months, 9 to 17 months, 18 to 59 months, and 60 months or older, aligned with Uganda’s national measles-rubella immunization schedule. Thirty-six additional facility-recorded cases could not be traced due to incomplete locator details. The study achieved an estimated statistical power of approximately 98 percent to detect an odds ratio of 0.30. In this enrolled sample, the median age was 37 months with an interquartile range of 17 to 61 months; 56 percent of cases were female compared to 45 percent of controls, while refugees constituted 51 percent of cases and 68 percent of the control cohort. While 25 percent of case-patients reported visiting a healthcare facility during the 7 to 21 days prior to rash onset compared to 16 percent of controls, this association was not statistically significant after analysis.

Multivariable conditional logistic regression demonstrated that social mixing in religious settings substantially increased infection risk, while vaccination conferred robust individual protection. Attendance at a place of worship within the incubation window of three weeks preceding symptom onset was associated with an 11-fold increase in the adjusted odds of measles infection compared with non-attendance, yielding an adjusted odds ratio of 11.1 with a 95 percent confidence interval between 3.5 and 35.1. Conversely, receipt of the first dose of the measles-rubella vaccine was associated with a 70 percent reduction in the odds of contracting measles relative to unvaccinated status, producing an adjusted odds ratio of 0.3 with a 95 percent confidence interval of 0.1 to 0.7. Receipt of a second vaccine dose provided even greater protection, showing a 95 percent reduction in odds with an adjusted odds ratio of 0.05 and a 95 percent confidence interval spanning 0.01 to 0.3.

Calculations of field vaccine effectiveness, conducted using the matched Mantel-Haenszel odds ratio among age-eligible participants, affirmed the biological efficacy of the intervention under field conditions. Among children aged 9 months and older eligible for the first dose, 50 percent of 64 cases had received at least one vaccine dose compared to 86 percent of 113 controls, resulting in a Mantel-Haenszel odds ratio of 0.07 and an estimated vaccine effectiveness of 93 percent, with a 95 percent confidence interval of 77 to 98 percent. For the second dose among children aged at least 18 months, vaccine effectiveness reached 95 percent, with a 95 percent confidence interval of 78 to 99 percent. These empirical findings aligned with global evidence establishing that measles-containing vaccines consistently demonstrate protective effectiveness exceeding 90 percent for a single dose and 95 percent for two doses, indicating that the sustained outbreak was not driven by vaccine failure.

Instead, the investigation revealed marked deficits in community vaccination coverage that allowed susceptible individuals to accumulate. Among eligible control children aged at least 9 months, coverage for the first vaccine dose was 67 percent overall, comprising 71 percent among national children and 66 percent among refugee children, an observed difference that was not statistically significant. However, coverage for the second dose dropped steeply to 36 percent across all eligible controls. A notable disparity emerged between demographic groups for the second dose: coverage reached 49 percent among refugee controls but stood at only 10 percent among national controls, a difference determined to be statistically significant. These figures diverged markedly from administrative reporting, where several subcounties reported administrative first-dose coverage exceeding 100 percent, highlighting the known limitations of administrative estimates that can arise from population movement, cross-boundary service utilization, and numerator-denominator mismatches.

The authors contextualized these results within the broader framework of measles epidemiology and immunization policy. With an estimated basic reproduction number ranging between 12 and 18, measles requires sustained population coverage of at least 95 percent with two doses of vaccine to establish herd immunity and interrupt transmission chains. In Kamwenge, the combination of administrative data discrepancies, low observed second-dose coverage among controls, and high-contact indoor congregation in places of worship created conditions conducive to protracted viral spread. The authors noted that displaced and refugee-hosting communities frequently confront structural barriers to healthcare, including physical movement, service disruptions, and challenges in continuity of care, which can generate acute localized pockets of susceptibility despite seemingly adequate district-level figures.

Several methodological limitations were documented by the investigators regarding the study design. Exposure and vaccination status assessments relied partially on caregiver recall when written child health cards were unavailable, introducing potential recall misclassification. Environmental observations were qualitative, performed by a single observer without a standardized scoring checklist, which may restrict comparative reproducibility. Because controls were sampled from neighboring households in affected localities, their coverage rates reflected local study communities rather than district-wide averages. Furthermore, serological testing was restricted to five initial cases under national surveillance protocols, meaning clinical case definitions were used for the broader cohort without universal laboratory confirmation. Despite these constraints, the study provides detailed empirical evidence that closing second-dose coverage gaps, improving health facility triage, and engaging community leaders at social gathering venues remain essential to controlling measles in mobile and refugee-hosting settings.

Subject of Research: Epidemiological investigation of a protracted measles outbreak in Kamwenge District, Uganda

Article Title: Protracted measles outbreak in a refugee-hosting setting in Kamwenge District, Uganda, 2025

Article References: Matovu, N., Migisha, R., Aman, K. D., Aujo, D., Nuwamanya, Y., Kwesiga, B., Bulage, L., Ssimbwa, B. N., Nsubuga, F., Ampeire, I., Atugonza, R., Baganizi, M., & Ario, A. R. (2026). Protracted measles outbreak in a refugee-hosting setting in Kamwenge District, Uganda, 2025. Discover Public Health, 23(1), Article 1753. https://doi.org/10.1186/s12982-026-03246-6

Image Credits: AI Generated

DOI: 10.1186/s12982-026-03246-6

Keywords: measles outbreak, Kamwenge District, Uganda, vaccine effectiveness, measles-rubella vaccine, refugee health, public health surveillance, epidemiology, Protracted, measles, outbreak, refugee-hosting