Lineage-matched Oropouche virus mRNA-LNP vaccines confer complete, cross-protective immunity in mice.

Oropouche virus (OROV) is an emerging orthobunyavirus responsible for recurrent and increasingly widespread outbreaks across South and Central America, including a recent epidemic that elevated global concern. In addition to its known neurotropic potential-manifesting as meningitis and encephalitis-OROV is now associated with vertical transmission and adverse pregnancy outcomes, underscoring its growing clinical and public health relevance. The rapid geographic expansion and extensive genetic diversification of circulating OROV lineages highlight the need for vaccine platforms that can be rapidly updated to match evolving strains. To address this challenge, we developed mRNA-lipid nanoparticle (mRNA-LNP) vaccines encoding OROV envelope glycoproteins from a historical prototype lineage (OROV BeAn19991; Brazil) and a recently circulating outbreak lineage (OROV AM0059; Brazil). Both immunogens were human codon-optimized, validated for robust expression, and evaluated in BALB/c and A129 mice. Vaccination elicited strong humoral and cellular responses, including high-titer OROV-specific IgG, broad cross-neutralization of prototype and contemporary strains, and potent CD4(+) and CD8(+) T cell immunity. Each vaccine conferred complete protection against lethal OROV challenge. Notably, the outbreak-lineage vaccine achieved full protection against both prototype and outbreak strains, whereas the prototype-based vaccine provided only partial cross-protection. These findings establish mRNA-LNP vaccines as a powerful and adaptable strategy for combating OROV. Incorporating contemporary, strain-matched antigens markedly enhances protective breadth and potency, positioning this platform for rapid deployment against ongoing outbreaks and the rising threat posed by related emerging orthobunyaviruses. IMPORTANCE: Oropouche virus (OROV) is a re-emerging orthobunyavirus that causes recurrent outbreaks across Central and South America. Although OROV infection is often described as a self-limited febrile illness, neurological complications and, more recently, fetal abnormalities and deaths have been reported, reflecting both the true clinical impact of OROV and improved surveillance. Despite this, no licensed vaccines or antivirals are available. Given the virus's segmented genome and extensive genetic diversity, an effective countermeasure must be both cross-protective and rapidly updateable as new lineages emerge. Here, we show that mRNA-lipid nanoparticle (mRNA-LNP) vaccines encoding OROV envelope glycoproteins from distinct viral lineages elicit strong antibody and T cell responses and provide robust protection in mouse models, including sterilizing immunity against lethal challenge with both prototype and currently circulating strains. Our data indicate that incorporating contemporary antigenic sequences can enhance cross-strain protection, supporting the use of mRNA-LNP platforms as a rapid, adaptable solution for future OROV outbreaks and related emerging pathogens.