Measles Outbreak in a Refugee Settlement, Kiryandongo District, Uganda, July– October 2023

Abstract

Background Measles is a highly infectious viral disease that mostly affects children. On 28 August 2023, the Ministry of Health (MoH) was notified of an outbreak of measles in Kiryandongo a refugee-hosting district, Western Uganda. We investigated to determine the scope of the outbreak, factors associated with transmission, strain, vaccine effectiveness (VE) and vaccine coverage (VC), and recommend evidence-based interventions. Method We defined a suspected case as onset of fever lasting ≥ 3 days and maculopapular rash with ≥ 1 of cough, coryza or conjunctivitis in a resident of Kiryandongo District, from July 1-October 25, 2023. A confirmed case was a suspected case with positive measles-specific IgM unexplained by vaccination the preceding 8 weeks. Case-patients were identified through medical records review and active community case search by snowballing. We conducted a 1:2 unmatched case-control study to evaluate risk factors for transmission. A control was a resident of Kiryandongo Refugee Settlement aged 4 months–6 years with no history of fever or rash from July 1‐October 25, 2023. We obtained crude and adjusted odds ratios (aORs) and their 95% confidence intervals, and calculated VC, and VE. We also conducted key informant interviews. Results We identified 74 case-patients (14 confirmed), 54% of whom were females and no deaths. The overall attack rate (AR) was 16/100,000 population and was higher among refugees than nationals (49 vs 11/100,000). Children < 12 months (AR:108/100,000) were the most affected age group. Genotyping results showed that it was a type B₃ measles strain. Being vaccinated (aOR:0.13, 95% CI:0.06–0.31) and playing around a water collection point (aOR:3.2, 95%CI:1.4–6.9) were associated with infection. VC was 87% among refugees and 89% among nationals; VE was 87% (95%CI:69–94) for both groups. Interviews with key staff revealed unrestricted movement of unregistered and thus unscreened refugees visiting their relatives in and out of the settlement. Conclusion This outbreak was associated with suboptimal vaccination coverage, congregating at water collection points, and accessing the settlement without screening. Isolation of measles infected children, increased screening of people entering the settlement and strengthening immunization programs could avert similar situations in future.