Osivax misses Phase 2b flu vaccine endpoint, shifts focus to combinations

Why it matters: The results are a setback for Osivax’s ambition to develop a standalone influenza vaccine targeting a conserved viral protein rather than the rapidly changing surface proteins targeted by conventional vaccines. However, the company believes its technology could still improve seasonal flu protection when combined with established vaccines.

By the numbers: The randomized, placebo-controlled Phase 2b Asuniva trial enrolled 2,850 healthy adults ages 18 to 59 in Belgium, France, Finland and Germany.

• OVX836 recorded a vaccine efficacy point estimate of 24%, which was not statistically significant.

• Secondary efficacy estimates were 28% against influenza-like illness as defined by the U.S. Centers for Disease Control and Prevention, 27% against influenza A/H3 and 25% against A/H1N1pdm09.

• The vaccine maintained a favorable safety profile and generated antibody and T-cell responses targeting the influenza nucleoprotein.

Osivax described the results as the first consistent efficacy signal across both major influenza A subtypes for a vaccine based solely on the nucleoprotein. However, none of the reported efficacy estimates establishes a statistically significant protective benefit, and the company did not disclose confidence intervals or detailed infection counts in its announcement.

How it works: Unlike traditional seasonal flu vaccines, which primarily target hemagglutinin, a surface protein that changes frequently, OVX836 targets the nucleoprotein, an internal viral protein that is much more conserved across influenza A strains.

• Osivax uses its oligoDOM nanoparticle platform to stimulate both antibody and T-cell responses against this protein. The goal is to generate broader protection that is less vulnerable to viral mutations.

What now: Rather than positioning OVX836 primarily as a standalone alternative, Osivax is highlighting its potential as an additional layer of protection alongside conventional flu vaccines.

• “Rather than replacing existing seasonal influenza vaccines, we believe the greatest opportunity lies in complementing them,” said Alexandre Le Vert, CEO and co-founder of Osivax.
• The strategy is not entirely new. In July 2025, Osivax published Phase 2a findings showing that administering OVX836 alongside GSK’s Fluarix Tetra was well tolerated and produced complementary immune responses without major interference. Those findings supported the feasibility of combining the approaches but did not establish improved clinical protection.

Also notable: In August, Osivax signed an agreement with South Korea’s GC Biopharma to develop a single-injection vaccine combining OVX836 with GC FLU, an established seasonal influenza vaccine.

• Under the agreement, Osivax leads global development and holds commercialization rights outside South Korea, while GC Biopharma supplies its vaccine and receives royalties. Financial terms were not disclosed. Osivax has also secured a second collaboration with an undisclosed global pharmaceutical company to pursue combination vaccines.

What to watch: While the Phase 2b trial suggests a possible protective effect across influenza A subtypes, the absence of statistically significant efficacy makes it uncertain how much additional protection OVX836 could deliver. Combining two vaccines that target different parts of the virus offers a plausible biological rationale, but evidence of complementary immune responses does not necessarily translate into better clinical outcomes.

What’s next: Osivax plans to advance its combination vaccine candidates through the two partnerships. The company has not disclosed a timeline for the next efficacy trial, which will need to establish whether adding OVX836 provides meaningful protection beyond that of conventional seasonal flu vaccines alone.