Ring and community vaccination for Bundibugyo ebolavirus outbreak response: a stochastic network modelling study

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Background: Vaccination with rVSV-ZEBOV is highly effective against Zaire ebolavirus, but protection against Bundibugyo ebolavirus (BDBV) is unproven. We evaluated the relative population impact and dose efficiency of a partially cross-protective hypothetical vaccine under operationally realistic constraints during a BDBV outbreak. Methods: We developed a stochastic transmission model on a two-layer household-community contact network calibrated to 2026 Democratic Republic of the Congo BDBV outbreak data. Time-varying effective reproduction numbers were estimated using a Bayesian renewal model. We evaluated case detection, isolation, contact tracing, reactive ring vaccination, and community vaccination (20-80% coverage). Base-case vaccine efficacy was 45% and included post-exposure protection against disease and mortality. Primary outcomes were mortality and incidence reductions, total doses, and dose efficiency (doses per death averted) over 90 days, evaluated in a probabilistic sensitivity analysis with 10,000 matched stochastic replicates per strategy. Results: Compared with base operations alone (30% detection, 30% tracing), enhanced operations alone (70% detection, 80% tracing) reduced expected mortality by 81.9% (95% UI 72.3-88.8). Reactive Ring 2 vaccination under base operations reduced mortality by 7.8% (4.7-10.9), requiring 89.5 doses per death averted. Added to enhanced operations, Ring 2 vaccination reduced mortality by 82.5% overall (73.0-88.9), an incremental benefit of 2.7% (0.9-4.9) beyond enhanced operations alone. Community vaccination at 20%, 40%, 60%, and 80% coverage reduced mortality by 44.4% (33.9-51.8), 67.9% (56.7-75.6), 80.4% (70.8-85.9), and 87.2% (79.6-91.3), requiring 40.3 to 80.9 doses per death averted. Interpretation: Strengthened case finding, contact tracing, and isolation averted most deaths even without vaccination. Once these operations were strong, reactive ring vaccination added little further benefit, whereas rapid community vaccination produced the largest reductions in simulated scenarios but required substantially more doses. A partially protective BDBV vaccine's population-level value will depend principally on rapid, broad delivery.

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