Vaccine Deployment and Ebola Transmission Dynamics Estimation in Eastern DR Congo

Abstract

Over the last 8 months, the Democratic Republic of the Congo (DRC) has reported nearly 600 cases of Ebola virus disease (EVD). Here, we estimate transmission dynamics associated with the outbreak, the percentage of the affected population that has thus far been effectively immunized (Imm) against EVD, and case count projections under three separate transmission scenarios.

After acquiring publicly available cumulative reported case counts of EVD, the Incidence Decay and Exponential Adjustment model was used to estimate the basic (R_0) and observed (R_Obs) reproduction numbers associated with the outbreak. R_0 and R_Obs estimates were then used to assess Imm and to project case counts under Base Case (i.e. no change), Better Case, and Worse Case transmission scenarios.

R_0 and R_Obs estimates range from 1.15 to 2.58 and from 1.10 to 1.63, respectively. These estimates suggest that approximately 4% to 37% of the affected population has thus far been effectively immunized against EVD; however, we also find that an Imm rate of 13% to 61% will need to be achieved to meet the estimated herd immunity threshold. Assuming no changes in transmission dynamics, we estimate that the expected cumulative case count will range between 982 and 1472 by late March 2019 (i.e. Base Case scenario); however, Better and Worse Case scenarios result in lesser and greater case count estimates, respectively.

Though >50,000 doses of rVSV-ZEBOV have already been deployed, vaccination efforts will need to be bolstered in the weeks ahead to eliminate EBOV transmission in the DRC. Under the assumption that rVSV-ZEBOV is the primary mode of transmission suppression within the context of this outbreak, another ~35,000 to ~100,000 doses will likely need to be deployed to achieve herd immunity.

Research reported in this work was supported by the National Institutes of Health through an NIH Director’s New Innovator Award DP2-MD012722.

Keywords: Ebola, Ebola Virus Disease, EVD, rVSV-ZEBOV, vaccination, DR Congo, Democratic Republic of the Congo, DRC