On 3 March 2020, a WHO supported cross-border rapid response investigation identified two presumptive positive cases of yellow fever in Kajo Keji county, Central Equatoria State, South Sudan. The initial Polymerase Chain Reaction (PCR) testing conducted at the National Public Health Laboratory in Juba, South Sudan tuned out negative. However, following further testing, both the cases were confirmed positive for yellow fever by plaque reduction neutralization testing (PRNT) at the regional reference laboratory, Uganda Viral Research Institute (UVRI) on 28 March.
The investigation was mounted in response to the recently declared outbreak in bordering Moyo district, Uganda. During the investigation, the team collected 41 blood samples from five villages which were in close proximity to the bordering Moyo district, Uganda. Of the 41 individuals whose samples were collected, nine (22%) had history of fever, but none had history of jaundice. The individuals represented a spectrum of occupations typical for the area (farming, forestry, homemaker, soldier). Most of the individuals investigated were between 20-45 years of age, and 18 (44%) of these individuals were female.