Vaccination Strategies for Ebola in the Democratic Republic of Congo: The WHO-Ebola Modeling Collaboration.

Objectives: Assess the effectiveness of ring vaccination in controlling an Ebola virus outbreak in the Democratic Republic of Congo.

Methods: This analysis focuses on two areas of the Democratic Republic of Congo, Beni and Butembo/Katwa, which were affected during the 2018-2020 Ebola outbreak. To simulate Ebola virus transmission, we used a spatially explicit agent-based model with households, health care facilities, and Ebola treatment units. Model parameters were calibrated using data collected under the ring-vaccination expanded-access protocol implemented during the outbreak. The model was used to estimate the impact of the deployed ring vaccination strategy, compared to what would have happened if there had been no ring vaccination. The impact of alternative vaccination strategies (mass vaccination, targeted geographic vaccination, and ring-plus) was evaluated as well.

Results: Compared to a hypothetical scenario where vaccination was not implemented, ring vaccination was estimated to have averted 54.3% (SD, 32.5%) and 62.7% (SD, 23.2%) of potential cases in Beni and Butembo/Katwa, respectively. Under ring vaccination, the average number of averted cases per 1000 vaccine doses administered was 15.1 (SD, 16.8) and 27.8 (SD, 22.9), in Beni and Butembo/Katwa, respectively. In terms of number of averted cases per vaccine dose, ring vaccination was estimated to be more efficient than any of the other evaluated vaccination strategies.

Conclusion: Despite some level of social instability, ring vaccination with the rVSV-ZEBOV vaccine was highly effective during the 2018-2020 Ebola outbreak in the Democratic Republic of Congo. As compared to alternative vaccination strategies, ring vaccination was estimated to be the most efficient.