Epidemiological investigation of measles outbreak in a refugee settlement in Lamwo District, Uganda

On 26^th September 2022, the Ministry of Health received a notification of a measles outbreak in Lamwo District. Eight (8) out of the eleven blood samples collected from suspected case-persons of Palabek Gem and Palabek Ogilli Sub-Counties for testing turned positive for measles-specific IgM antibodies at the UVRI. On 29^th September 2022, a team of Epidemiologists from the Ministry of Health was deployed. We conducted an epidemiological investigation to determine the scope of the outbreak, and associated risk factors to prevent further transmission. We defined a probable and confirmed case in line with Uganda's national technical guidelines for integrated disease surveillance and response. We reviewed outpatient and inpatient health facility records of all health facilities to generate a line list from 1^st July to 30^th September 2022. We then conducted a case-control study, with Mantel Haenszel odds ratios to determine the factors associated with the outbreak. The study identified fifty-six measles cases (48 probable and eight confirmed), with 54% being male, and 89% being South Sudanese nationals. The highest attack rate was among children <1 year (51/10,000) and Zone 8 parish in the Palabek Refugee Settlement (72/10,000). The index case was a 6-year-old South Sudanese boy who entered Uganda on 7^th July 2022 and later developed symptoms on 24^th July 2022. In this study, we estimated vaccination coverage and the vaccine effectiveness at 63% and 72%, respectively. Malnutrition (ORMH=3.73, 95% CI: 1.22-11.43) and receiving one or no doses of measles vaccine (ORMH=7.0, 95% CI: 2.8-17.6) were the risk factors. We recommended mass administration of vitamin A supplementation and a measles vaccine dose to children under five years of age regardless of the vaccination status. To prevent future outbreaks, we recommended improvement of nutrition and implementation of periodic measles follow-up vaccination campaigns.