Osivax has vaccinated the first participant in a randomized, double-blind, multicenter phase 2b clinical trial (NCT05569239) evaluating OVX836, a broad-spectrum influenza A vaccine candidate. The study will assess efficacy, safety, and immunogenicity during the upcoming flu season.
The trial plans to enroll approximately 2,850 adults aged 18–59 at 16 sites across multiple European countries. Participants will be randomly assigned under blinded conditions, and outcomes will include laboratory-confirmed influenza as well as prespecified immunologic endpoints.
OVX836 targets the influenza A nucleoprotein (NP), a conserved internal antigen intended to broaden protection across strains. The candidate employs Osivax’s oligoDOM™ platform to present NP as a self-assembling nanoparticle designed to elicit robust T-cell and B-cell responses.
In an email Q&A with the Osivax team, we discussed the phase 2b trial and development plans. They discussed endpoints, breadth/durability, and potential US use.
Contagion: What is the primary efficacy endpoint and case definition (e.g., PCR-confirmed symptomatic influenza A), how is the study powered, and how will safety and immunogenicity be assessed alongside efficacy?
Osivax team: "The primary efficacy endpoint is defined as first occurrence of RT-PCR-confirmed influenza Type A symptomatic disease with a protocol-defined case definition.:
"The study will have 80% power to demonstrate a vaccine efficacy of 50% with a lower limit of the 95% confidence interval superior to 0%, taking into account an attack rate of 3.8% in the placebo group."
"The vaccine safety will be assessed in all participants through solicited local and systemic adverse events within 7 days after vaccination, unsolicited adverse events up to Day 29, serious adverse events (SAEs), adverse events of special interest (AESIs), new onset of chronic diseases (NOCDs), and medically attended adverse events (MAAEs) throughout the entire study (up to 10 months). The immune response will be assessed in a subset of 56 participants using blood samples collected at Day 1 (pre-vaccination) and Day 8. These assessments will include cell-mediated immune response measured by ELISPOT assay for IFN-γ secretion by PBMC, Flow cytometry (ICS) for NP-specific CD4+ and CD8+ T-cells expressing IL-2, TNFα, and/or IFNγ, and finally the humoral immune response measured by ELISA to quantify anti-nucleoprotein IgG levels in serum."
What You Need To Know
Primary endpoint is first occurrence of RT-PCR–confirmed symptomatic influenza A, with 80% power to show 50% vaccine efficacy assuming a 3.8% placebo attack rate.
Safety is tracked through solicited and unsolicited adverse events and serious events, while immunogenicity is measured in a 56-participant subset using ELISpot, ICS, and anti-NP IgG ELISA.
Cross-strain breadth and durability are not assessed in this trial, and current plans envision pairing OVX836 with standard inactivated influenza vaccines in the US pending results.
Contagion: Since OVX836 targets the conserved nucleoprotein (NP), which cellular and humoral readouts will you use to evaluate cross-strain breadth and durability, and how do these map to signals seen in prior Phase 1/2a studies?
Osivax team: "The trial is not designed to evaluate cross-strain breath and durability of protection. Cross-reactivity of the response was previously studied in a Ph2a clinical trial and showed high cross-reactivity with all A strains tested (H1N1, H3N2 H5N1)."
"The durability of the clinical vaccine efficacy will be a matter of future studies in the Clinical Development plan, as well as the confirmation of the signal of vaccine efficacy observed in previous studies."
Contagion: What are your U.S. development plans (potential US sites or bridging strategy, FDA interactions, BARDA/NIH alignment), and how do you envision OVX836 being used in the US if efficacy is confirmed (stand-alone or combined with standard quadrivalent flu vaccines)?
Osivax team: "Development plans will be based on future results and are being discussed with regulatory agencies such as the FDA, the EMA and other international regulatory agencies."
"Regarding use in the US, we currently anticipate OVX836 to be combined with standard IIV in order to capitalize on complementary mechanisms of action."
Earlier Phase 1 and Phase 2a studies (>1,400 participants) have shown acceptable safety, immunogenicity, cross-reactivity, and exploratory signals of efficacy, supporting progression to large-scale efficacy testing. Investigators note the ongoing public health burden of seasonal influenza and the need for improved vaccine strategies.
Reference
Osivax Announces First Participant Vaccinated in Phase 2b Trial Evaluating Broad-Spectrum Influenza A Vaccine Candidate, OVX836. September 16, 2025. Accessed September 23, 2025. https://www.globenewswire.com/news-release/2025/09/16/3150564/0/en/Osivax-Announces-First-Participant-Vaccinated-in-Phase-2b-Trial-Evaluating-Broad-Spectrum-Influenza-A-Vaccine-Candidate-OVX836.html
