Modeling the Impact of Vaccine Delivery on the 2018-2019 North Kivu & Ituri Ebola Outbreak

Background: The reemergence of Ebola in the Democratic Republic of Congo (DRC) has developed into the largest and most challenging Ebola Virus Disease (EVD) outbreak in the country's history. Violence has hindered response efforts, including the administration of the investigational EVD vaccine, rVSV-ZEBOV. During a crisis of this magnitude, decision-makers often look to predictive models to inform operational strategy. Methods: We used an agent-based model to forecast the additional EVD case burden in North Kivu & Ituri health zones, by the end of July 2019, at different levels of vaccine administration and contact-finding. Our model incorporated countermeasure strategies like social distancing, school closure, hospital isolation, and ring vaccination, while varying rates of contact-finding and vaccine administration to generate case incidence estimates. Findings: Our model estimated that if the response continues as-is, approximately 1,039 additional cases will occur between May 20th and July 31st, for a cumulative total of 2,688 EVD cases by the end of July. If vaccine administration were discontinued, we estimated a 13.4% higher incidence of EVD cases by the end of July. Increased contact-finding and vaccination administration resulted in 10.3% fewer additional EVD cases. Interpretation: Near real-time forecasting can generate potential outbreak trajectories dependent on the magnitude and success of public health response efforts. Although the ongoing vaccination campaign has reduced the overall number of EVD cases that would be expected in the ongoing outbreak, simultaneous delivery of other countermeasures at high rates is necessary to bring the outbreak to a close. While our projections should be interpreted cautiously due to evolving outbreak dynamics, the estimated magnitude can be used to inform public health response planning for the international community. Funding Statement: This study was funded by the Defense Threat Reduction Agency's (DTRA) Technical Reachback contract, (HDTRA1-09-D-0009-0003) and the contract to Virginia Polytechnic Institute and State University (HDTRA1-17-D-0023-0001). Declaration of Interests: All authors declare they have nothing to disclose.