A bivalent Adenovirus-Vectored Vaccine induces a measurable humoral response, but does not protect cynomolgus macaques against a lethal challenge with Sudan virus

The most recent Sudan virus (SUDV) outbreak in Uganda was first detected in September 2022 and resulted in 164 laboratory-confirmed cases and 77 deaths. Currently, there are no approved vaccines or therapeutics against SUDV. In the current study, we investigated the protective efficacy of ChAdOx1-biEBOV in cynomolgus macaques using a prime or a prime-boost regimen. ChAdOx1-biEBOV is a replication-deficient simian adenovirus vector encoding SUDV and Ebola virus (EBOV) glycoproteins (GPs) at the E1 and E4 loci, respectively. Intramuscular vaccination induced SUDV and EBOV GP-specific IgG responses and neutralizing antibodies. Upon challenge with SUDV, vaccinated animals, regardless of vaccination scheme, showed signs of disease like those observed in control animals, and no difference in survival outcomes were measured among all three groups. Viral load in blood samples and in tissue samples obtained after necropsy were not significantly different between groups. Overall, this study highlights the importance of evaluating vaccines in multiple animal models, including nonhuman primates, and demonstrates the importance of understanding protective efficacy in both animal models and human hosts.