Leyden Labs adds €40m for intranasal flu prevention

Why it matters: The financing adds further momentum to one of Europe’s more closely watched respiratory virus prevention companies, as investors continue to back antibody-based alternatives and complements to seasonal vaccines.

• The new investment comes from the European Innovation Council Fund, Invest-NL, the Gates Foundation, ClavystBio and others. Leyden Labs said the syndicate spans Europe, the US and Asia and will support development of its mucosal protection platform, which is designed to deliver broadly protective antibodies directly to the respiratory mucosa.

How it works: Leyden Labs is developing intranasal antibody sprays intended to block respiratory viruses at the point of entry. The company argues that this local delivery strategy could provide immediate protection in the nose and mouth, where airborne viruses such as influenza and coronaviruses typically begin infection.

Zoom in: The company’s lead programme, PanFlu, is built around CR9114, a broadly neutralising anti-influenza antibody that targets a conserved region of the influenza virus haemagglutinin (HA) protein. Rather than positioning CR9114 as a conventional systemic antibody, Leyden is trying to use it locally through the nose.

• Systemically delivered antibodies have long been explored for influenza, but broad seasonal prevention is difficult because of dose, cost and delivery logistics. Leyden’s thesis is that concentrating antibodies at the site of viral entry could lower the practical barriers to prophylaxis.
• Leyden Labs has already reported early human safety data for its intranasal flu prevention antibody. In two phase 1 trials involving 143 healthy volunteers, intranasal administration was shown to be safe and tolerable, and the antibody was detected locally in the nasal cavity after dosing. The data did not yet include human efficacy endpoints, leaving prevention of infection as the key next test for the programme.

The bigger picture: Leyden Labs has been on a fundraising run. In October 2025, the company raised €30m from the EIC Fund and Invest-NL to advance PanFlu and broader mucosal pipeline work. That followed a $70m Series B announced earlier in 2025 and a €20m European Investment Bank venture debt investment facilitated by HERA.

• The latest €40m round broadens the investor base further, adding the Gates Foundation and Singapore-based ClavystBio alongside European public investors. The Gates Foundation’s involvement is particularly notable because Leyden said the investment will support work on access strategies for low- and middle-income countries.

Yes, but: Leyden still has to prove that its approach can prevent disease in humans. The company has generated safety and local-delivery data, while its efficacy case still leans on preclinical and non-human primate results. The next question is whether intranasal antibodies can translate into meaningful protection in clinical efficacy studies.

Competition is heating up: Leyden is not the only company attracting capital for antibody-based flu prevention. London-based RQ Bio has just raised $115m in Series A financing to advance RQB01, a long-acting antibody designed to provide broad protection against influenza. RQ Bio says its candidate is in IND-enabling studies and is designed for extended duration of action, with the aim of protecting vulnerable patients for an entire flu season after a single administration.

• The field is also drawing strategic interest from larger drugmakers. Cidara’s late-stage flu prevention candidate CD388 has generated enough interest to support MSD’s $9.2bn acquisition of the company, while Moderna is seeking to challenge traditional egg- and cell-based flu vaccines with an mRNA alternative.
• The nasal-prophylaxis field is also expanding beyond antibodies. NorthLinks Bio launched this week with a $34m financing from RA Capital Management to advance HEX17, a self-administered intranasal antiviral designed to block respiratory virus entry through a host-directed, glycan-targeted mechanism. The company is effectively a US-managed relaunch of UK-based Pneumagen Ltd., which reorganised into Boston-based NorthLinks Bio while keeping research operations in St Andrews, Scotland.

The bottom line: Leyden Labs’ new €40m raise is less about a single financing event than the continuation of a broader bet: that flu prevention will need more than vaccines, especially for older and immunocompromised people. The company now has money, public-health investors and early human safety data behind its nasal spray strategy. What it still needs is clinical proof that local antibody delivery can stop respiratory viruses where they enter.