A Nasal Shield Against the Flu? Leyden Labs' New Spray Shows Promise

LEIDEN, The Netherlands – February 04, 2026 – In the ongoing battle against respiratory viruses, a Dutch biotechnology firm may be on the verge of a paradigm shift. Leyden Laboratories B.V. has unveiled landmark data suggesting a simple nasal spray could provide immediate and broad protection against influenza, potentially changing how we protect ourselves from seasonal and pandemic threats.

Published in the prestigious journal Science Translational Medicine, the research details the successful initial testing of an antibody-based nasal spray designed to neutralize the influenza virus at its primary point of attack: the nasal passages. The findings provide a robust proof-of-concept for the company's PanFlu program, an ambitious effort to stop infections before they can even begin.

A New Frontier in Flu Prevention

The newly published data consolidates results from three critical studies. In two separate Phase 1 clinical trials involving a total of 143 healthy volunteers, the PanFlu nasal spray was found to be safe and well-tolerated. The studies tested various single and repeated dosing schedules for up to 14 days. Critically, repeated dosing achieved high and sustained concentrations of the active antibody, CR9114, directly in the nasal cavity, overcoming the body's natural clearance mechanisms. Follow-up analysis confirmed that the antibody remained fully functional and capable of neutralizing viruses after residing in the nasal mucosa.

A third study in non-human primates provided compelling evidence of the spray's protective power. Animals that received the intranasal CR9114 antibody were potently protected from infection and viral replication after being exposed to the H1N1 influenza virus. They showed significant reductions in viral load compared to those who received a placebo, validating that the antibody levels achieved in the nose can confer meaningful protection in a highly translatable animal model.

“These results demonstrate the feasibility of our ongoing efforts to stop viruses at the portal of entry rather than through the traditional route of intravenous or intramuscular delivery,” said Clarissa Koch, Chief Scientific Officer of Leyden Labs, in the company's announcement. “Our lead candidate for PanFlu contains CR9114, the broadest human monoclonal influenza antibody identified to date. These new data across species provide important validation of our approach.”

Beyond the Annual Shot: A Tool for the Vulnerable

While not intended to replace annual flu shots, Leyden Labs' approach offers a powerful complement to existing public health strategies. Traditional vaccines are a cornerstone of flu prevention, but they require several weeks to stimulate an effective immune response and their effectiveness can vary depending on the match with circulating strains. Furthermore, they are less effective in people with weakened or compromised immune systems.

This is where an antibody-based nasal spray could fill a critical gap. By delivering a pre-made, broadly effective antibody directly to the site of infection, the spray provides what is known as passive immunity. This protection is immediate and does not require the recipient's body to mount its own immune response. This makes it a potentially game-changing tool for the elderly, infants, cancer patients undergoing chemotherapy, and other immunocompromised individuals who remain vulnerable despite vaccination.

“As we once again face a challenging influenza season, there is a growing need for additional tools that complement vaccination and help people better protect themselves,” remarked Boris Juelg, MD, PhD, a key figure in the research. “Our findings show that a simple intranasal spray of the CR9114 antibody rapidly achieves effective levels, is well tolerated, and exhibits strong antiviral activity... underscoring the promise of CR9114 as an innovative strategy to stop influenza infections before they begin.”

The Science of a Mucosal Shield

The innovation behind Leyden Labs' product lies in both what it delivers and how it delivers it. The active ingredient, CR9114, is a human monoclonal antibody that targets a highly conserved, stable part of the influenza virus known as the hemagglutinin (HA) stalk. While the 'head' of the HA protein mutates rapidly from season to season—the reason flu shots must be updated annually—the stalk region remains largely unchanged across a vast array of influenza A and B strains. By targeting the stalk, CR9114 can neutralize not only common seasonal flu viruses but also potentially pandemic strains, including H5N1 avian influenza, against which it has shown efficacy in preclinical models.

Delivering this antibody through a nasal spray directly targets the mucosal surfaces of the nose and throat, creating a protective barrier right where airborne viruses first try to enter the body. This approach has long been a goal for virologists but has faced significant technical hurdles, primarily the rapid clearance of substances from the nasal passages.

“Administering antibodies by the mucosal route may prove particularly effective for respiratory viruses so that the antibodies can neutralize virus at the mucosal portal of entry,” noted Dan Barouch, MD, PhD, of Beth Israel Deaconess Medical Center and a co-author on the paper. The success of Leyden Labs in achieving sustained antibody concentrations represents a key breakthrough in making this strategy viable.

A Strategic Bet on Universal Protection

Leyden Labs is positioning its 'Mucosal Protection Platform' as a new paradigm in infectious disease prevention, with ambitions that extend beyond influenza. The company is developing a portfolio of nasal sprays targeting other respiratory threats, including coronaviruses. This strategic vision has attracted significant financial backing from a global syndicate of high-profile investors. The company has raised over $100 million in the last two years from backers including Polaris Partners, GV (formerly Google Ventures), and ClavystBio, a firm established by Singapore's sovereign wealth fund Temasek. This funding is fueling the advancement of PanFlu into Phase 2 human efficacy studies and expanding the company's pipeline.

The company’s strategy also includes key partnerships. The CR9114 antibody itself was licensed from Janssen Pharmaceuticals, a Johnson & Johnson company, in 2022. This combination of a promising, broadly acting antibody with a novel delivery platform places Leyden Labs at the forefront of a new class of prophylactic therapies.

With the successful completion of these initial studies, the path is now clear for the next phase of clinical development. While regulatory hurdles for a novel biologic-device combination remain, the compelling data provides a strong foundation for moving forward. If successful in larger trials, this nasal shield could become an essential tool in the public health arsenal, offering a new way to protect individuals, families, and entire communities from the persistent threat of respiratory viruses.