Mosnodenvir, a promising Phase 2a-tested oral antiviral against dengue with demonstrated antiviral activity in humans, is ready to move into a new phase of development. All rights to mosnodenvir have been transferred back to KU Leuven. As a next step, KU Leuven and the Centre for Drug Design and Discovery (CD3) aim to identify partners to build on more than a decade of research and extensive preclinical and clinical studies with mosnodenvir. In a new study published this week in The New England Journal of Medicine, professor Anna Durbin (Johns Hopkins University) and colleagues report findings that further demonstrate the efficacy for mosnodenvir against dengue infections, including its potential for once-weekly dosing. Since there are no antiviral drugs against dengue, mosnodenvir may address a major unmet global health need.
- Dengue is a major and growing global health threat, with an estimated 400 million infections and 100 million people developing dengue disease each year. Close to 4 billion people in over 129 countries are at risk.
- There is no antiviral drug to prevent or treat dengue, leaving a major unmet global health need.
- Mosnodenvir is an orally available small-molecule antiviral with equipotent activity against all four dengue virus serotypes.
- Mosnodenvir is the first antiviral drug candidate with proven activity against dengue in humans; as demonstrated in a Phase 2a human challenge study published in 2025 in The New England Journal of Medicine.
- New clinical findings, also published in The New England Journal of Medicine, further strengthen the evidence for mosnodenvir, including its potential for once-weekly dosing.
- Mosnodenvir has been dosed to about 900 people, it is safe and well tolerated.
- The rights to this advanced drug candidate are returned to KU Leuven allowing mosnodenvir its further development.
- A promising drug for a growing global health challenge
Dengue is one of the world’s fastest-growing infectious disease threats with approximately 400 million infections each year. While the greatest burden remains in tropical and subtropical regions, locally acquired dengue cases have also increased in Europe in recent years, particularly in southern Europe. Climate change creates increasingly favourable conditions for the mosquitoes that transmit the virus.
Yet there is still no specific antiviral treatment or prophylactic drug available for dengue.
Mosnodenvir may help fill that gap. The oral small-molecule antiviral originated from joint research efforts from the Laboratory of Virology and Antiviral Research at the Rega Institute and drug discovery experts at the Centre for Drug Design and Discovery (CD3) of KU Leuven with financial support from Wellcome.
The programme was subsequently advanced by a global pharmaceutical company and underwent extensive preclinical and clinical development. In a Phase 2a controlled human infection study [Durbin et al., The New England Journal of Medicine (2025)] treatment with mosnodenvir significantly reduced the number of infected individuals and lowered dengue virus levels in those who were infected, compared with placebo-treated participants. New clinical findings reported by Prof. Anna Durbin (Johns Hopkins Bloomberg School of Public Health) and colleagues confirm the dose-dependent antiviral activity of daily mosnodenvir and extend these findings to once-weekly dosing [Van Wesenbeeck et al., The New England Journal of Medicine (2026)]. More than 900 people received mosnodenvir in studies to date, with no safety concerns identified.
An opportunity to take an advanced programme forward
The rights to the programme have recently reverted to KU Leuven, creating a new opportunity to take this advanced drug candidate forward. Together with Wellcome, we are now seeking a partner with the expertise and capacity to continue the development of mosnodenvir.
“This is a rare opportunity to build on a decade of drug discovery and development rather than to start from scratch,” says Dr. Patrick Chaltin, Managing Director of CD3. “Mosnodenvir has already demonstrated antiviral activity in humans. We now need the right partner to build on that evidence and take the programme through the next stages towards patients.”
“When we started this research more than 10 years ago, there was no guarantee we would ever get this far,” says Prof. Johan Neyts of the KU Leuven Rega Institute. “Seeing a molecule that originated in our laboratory demonstrate antiviral activity in people, even following once weekly dosing, is exactly why we keep searching for new ways to tackle infectious diseases.”
“Mosnodenvir has the potential to make a real difference to people living with the constant threat of dengue,” says Dr. Sally Nicholas, Head of Vector Control and Therapeutics at Wellcome. “An effective antiviral could add a much-needed tool in the fight against dengue. We now have an opportunity to bring one closer to the people who need it.”
CD3, KU Leuven and Wellcome remain strongly committed to move the development of mosnodenvir forward and are looking for the right partner to do so.
Contact details:
Sooike Stoops, CD3 communication
Relevant publications:
- Daily Mosnodenvir as Dengue Prophylaxis in a Controlled Human Infection Model – NEJM, 2025
- Once-Weekly Mosnodenvir as Dengue Prophylaxis in a Human Infection Model – NEJM, 2026
Programme information:
