Cross-protection against Bundibugyo by Ebola and Sudan vaccines

Ebola outbreaks continue to expand across Central Africa, yet available countermeasures remain limited and virus-specific. Whether available vaccines developed against the related Ebola virus (EBOV) and Sudan virus (SUDV) can confer cross-protection against Bundibugyo virus (BDBV) is incompletely understood. Here, we developed a BDBV surrogate challenge model and evaluated cross-protective immunity conferred by a set of monovalent vaccine candidates representing all three Orthoebolavirus species affecting humans. A yellow fever 17D-vectored BDBV vaccine (YF-BDB) expressing the BDBV glycoprotein (GP) as antigen conferred homologous protection in Ifnar-/- mice, preventing systemic viral dissemination and providing survival following surrogate BDBV challenge. Intriguingly, also vaccination with YF-EBO or YF-SUD protected mice from such BDBV surrogate challenge. Conversely, while YF-BDB and YF-EBO fully protected against respective heterologous EBOV or BDBV infection, they conferred only partial protection against lethal challenge in a comparable SUDV model. Serological analyses revealed comparable titers of cross-reactive antibodies across all vaccine groups. However, neutralization, especially cross-neutralization, was limited suggesting a major role for non-neutralizing mechanisms in protection. These findings demonstrate asymmetry in cross-protective immunity among Orthoebolavirus vaccines and indicate that SUDV GP-based antigens may provide broader protection than EBOV- or BDBV-targeted candidates. However, our data add to the preliminary yet limited evidence that EBOV GP-based vaccines might offer at least some degree of protection against BDBV, the virus driving current Public Health Emergency of International Concern (PHIEC) in the Central-East Africa region.