Addressing Key Issues in Developing Safe and Effective Oropouche Virus Vaccines

Dear Editor,

The recent geographic expansion of Oropouche virus (OROV) across Latin America and the Caribbean has transformed a historically neglected arbovirus into an emerging public health concern, placing vaccine development on regional and global health agendas. However, rational vaccine design requires clarifying key issues in immunogenicity, pathogenicity, and evolutionary dynamics, including the potential influence of immunity against closely related orthobunyaviruses. Herein, we discuss critical knowledge gaps in these areas that must be addressed to guide OROV vaccine development efforts.

A major concern is the potential antigenic divergence among OROV strains, particularly in reassortant viruses, which have been increasingly reported during recent outbreaks [1, 2, 3]. Available evidence remains conflicting and supports two competing interpretations: reassorted OROVs might undergo sufficient antigenic divergence to enable immune escape, resulting in antigenically distinct viral variants or potentially different serotypes; or reassorted OROVs might maintain a largely conserved antigenic profile, allowing protective cross‐immunity and suggesting a single OROV serotype. Beyond its implications for vaccine development, the antigenic complexity of OROV would also pose challenges for other preventive approaches, such as monoclonal antibodies (mAbs), which target narrower epitope repertoires than vaccines.

The hypothesis of multiple serotypes is consistent with evidence of immune escape between the prototype strain (BeAn19991) and contemporary reassorted OROV [3, 4]. Conversely, serum samples collected between 2002 and 2020 in Brazil, Colombia, Costa Rica, and Peru demonstrated marked neutralization against different OROVs, including BeAn19991 and reassorted strain [2]. Cross‐neutralization among viruses circulating across different years and geographic settings, presumably under different selective pressures, aligns with the single‐serotype hypothesis. Interestingly, cross‐neutralization has also been demonstrated even between distinct orthobunyaviruses [5], suggesting conserved epitopes both within and between viral species.

These divergent results highlight the need for rigorous antigenic and serological characterization of OROV, including possible antibody‐dependent enhancement (ADE), which remains a hypothetical concern. If the circulation of multiple OROV serotypes is demonstrated, careful surveillance would be needed to identify the public health‐relevant serotypes. Vaccine antigens should then be aligned with the most epidemiologically important strains, while considering the potential risk of enhanced disease associated with other viral strains. On the other hand, if OROV is shown to comprise a single serotype, immunization with a single antigenic variant could provide protection against other lineages/genotypes. Even in this latter scenario, continuous monitoring of OROV evolution would be essential to identify emerging lineages. Although still belonging to the same serotype, such lineages could exhibit sufficient antigenic divergence to justify updating or adding vaccine antigens. Given these uncertainties, flexible vaccine platforms that allow rapid antigen updates or target more conserved immunogenic regions of the OROV glycoproteins should be prioritized [6].

In addition to investigating intra‐OROV antigenic relationships, it is crucial to determine whether pre‐existing immunity to other human‐infecting Orthobunyavirus oropoucheense members, such as Iquitos (IQTV) and Madre de Dios (MDDV) viruses, could influence OROV vaccine performance, including potential ADE. Vaccine performance should therefore be evaluated not only in OROV‐endemic regions, but also in regions where IQTV and/or MDDV co‐circulate, particularly in western Amazonia (Figure 1).

Figure 1.

Geographic distribution of Oropouche (OROV) and conspecific viruses [Iquitos (IQTV) and Madre de Dios (MDDV) viruses] in the Americas. OROV, IQTV, and MDDV have a three‐segmented genome comprising the small (S), medium (M), and large (L) segments. IQTV and MDDV are naturally occurring reassortant viruses containing OROV‐derived S and L segments and M segment from unidentified orthobunyaviruses. IQTV has been reported in humans, whereas OROV and MDDV have been detected in both humans and non‐human primates. Epidemiological data were compiled from selected references [1, 2, 7].

The persistence of immunity against OROV is another key aspect that requires investigation in well‐designed longitudinal studies. Although studies in non‐human primates suggest that prior exposure to OROV confers protection against reinfection for up to 524 days [8], data on the durability of immunity against orthobunyaviruses remain limited. Schmallenberg virus (SBV) is one of the best‐characterized orthobunyaviruses regarding long‐term immunity. In studies conducted with naturally or experimentally infected animals, immunity against SBV has been shown to persist for at least 2 years and protect against reinfection for at least 16 months [9, 10]. Extrapolation to OROV is uncertain; however, these findings suggest that long‐lasting protective immunity within orthobunyaviruses is biologically plausible. Clarifying the duration of immunity in both naturally exposed and vaccinated individuals will therefore be essential for defining optimal vaccination schedules and booster strategies.

The possibility of OROV harming fetal development is another important issue for vaccinology. Recent reports have raised concerns about adverse fetal outcomes following OROV infection [11]; however, a causal relationship and the underlying pathogenic mechanisms have not yet been clearly established. In the absence of definitive evidence, vaccine design should follow a precautionary approach, favoring non‐replicating vaccine platforms for immunizing pregnant women or women of childbearing age, such as mRNA vaccines or replication‐incompetent viral vectors. Notably, despite their potential advantages, these platforms should be carefully evaluated for safety, particularly during pregnancy. Furthermore, OROV vaccines should ideally induce long‐lasting immunity to prevent vertical transmission and, if administered during pregnancy, elicit a rapid protective immune response to avoid fetal risk. The latter requirement should be carefully evaluated in clinical trials, taking into account pregnancy‐associated immunological modulation.

Finally, the development of effective vaccines is challenged by substantial gaps in our understanding of OROV's molecular biology, evolutionary dynamics, and pathogenicity, reflecting decades of relative neglect. A precautionary framework that accounts for each of these uncertainties is essential to guide vaccine development and implementation in endemic settings. In parallel, mAb‐based strategies targeting OROV should also be explored, similar to those investigated for other arboviruses [12].

Author Contributions

José Valter Joaquim Silva Júnior: conceptualization, literature search, writing – original draft, and writing – review and editing. Edmilson F. de Oliveira‐Filho: conceptualization, literature search, figure, writing – review and editing. Jan Felix Drexler: discussion, literature search, supervision and writing – review and editing.

Ethics Statement

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Silva Júnior J. V. J., de Oliveira‐Filho E. F., and Drexler J. F., “Addressing Key Issues in Developing Safe and Effective Oropouche Virus Vaccines,” Journal of Medical Virology 98 (2026): e71132. 10.1002/jmv.71132.

Data Availability Statement

The authors have nothing to report.