Single-dose replicon RNA Sudan virus vaccine uniformly protects female guinea pigs from disease.

The Sudan virus (SUDV) outbreaks in Uganda in 2022 and 2025 created public health concerns in-country and the entire East African region. There are currently no licensed countermeasures against SUDV. We developed a SUDV vaccine candidate based on a nanocarrier (LION(TM)) complexed with an alphavirus-based replicon RNA. Here, we compare the protective efficacy of the LION-SUDV vaccine either encoding the SUDV glycoprotein (GP) alone or in combination with the Ebola virus (EBOV) GP (LION-Combination). A LION-EBOV vaccine which is protective against EBOV was also included to determine the potential for cross-protection against SUDV infection. Single-dose vaccinations were conducted three weeks before challenge with a lethal dose of guinea pig-adapted SUDV using a female guinea pig disease model. We demonstrate 100% survival and protection with the LION-SUDV and the LION-Combination vaccines, while the LION-EBOV vaccine achieved 50% protection. Antigen-specific humoral responses correlate with decreased virus replication and survival. This result warrants further studies in larger animal species to ensure that protective efficacy is maintained with the single-dose LION-SUDV vaccine.