Implementing an intra outbreak ring vaccination clinical trial for Sudan Ebola virus disease within four days of outbreak notification in Uganda.

East and Central Africa experiences heightened threats for Ebola Virus Disease (EVD), with the latest outbreak caused by the Bundibugyo ebolavirus (BDBV) reported in the Democratic Republic of the Congo (DRC) and Uganda on 15th May 2026. The BDBV outbreak comes just over a year following the declaration of Sudan Virus Disease (SVD) outbreak in Uganda on 30th January 2025. Following the 2025 outbreak, a race against the clock mobilization occurred over the subsequent four days to launch a ring vaccination trial for a candidate vaccine against SVD. During this four-day period, the investigation team leveraged ongoing engagements with trial sponsors to activate prefinancing mechanisms and unlock in-kind financing from the government of Uganda. Further, the team activated a prepositioned research protocol to secure rapid ethics and regulatory clearance, and quickly accessed investigation product within the country, supportive ethics/regulatory systems, presence of logistical and data management systems established during the 2022 outbreak, collaborative relationship between the trial and the Ministry of Health outbreak response teams. Finally, previously trained field and community engagement personnel were mobilized overnight, offered refresher training and rapidly deployed to the field. In conclusion, the unprecedented four-day turnaround was made possible by the research, logistical and staffing capacities established during the 2022 SVD outbreak, an achievement that offers a blueprint for rapid evaluation of medical countermeasures during outbreaks.