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