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

Vaccination with rVSV-ZEBOV is highly effective against Ebola virus, but protection against Bundibugyo virus (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.

We developed a stochastic transmission model on a clustered household-community contact network with empirically realistic local structure, calibrated to 2026 DR 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 (Ring 1: direct contacts of the index case; Ring 2: contacts of contacts), and community vaccination (20-80% coverage). Base-case vaccine effectiveness 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.

Compared with base operations alone (30% detection, 30% tracing), enhanced operations alone (70% detection, 80% tracing) reduced expected mortality by 81·6% (95% uncertainty interval 73·1-87·7). Reactive Ring 2 vaccination under base operations reduced mortality by 24·6% (18·0-29·6), requiring 35·1 doses per death averted. Added to enhanced operations, Ring 2 vaccination reduced mortality by 83·6% overall (76·4-89·0), an incremental benefit of 10·5% (6·2-15·6) beyond enhanced operations alone. Community vaccination at 20%, 40%, 60%, and 80% coverage reduced mortality by 44·7% (34·8-52·5), 67·4% (56·2-74·3), 79·8% (70·4-85·3), and 86·6% (79·2-90·4), respectively, requiring 53·8-111·4 doses per death averted.

Strengthened case finding, contact tracing, and isolation averted most deaths even without vaccination. Once these operations were strong, reactive ring vaccination added a modest 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.

Canadian Institutes of Health Research.

For the French translation of the abstract see Supplementary Materials section.