Dengue antiviral mosnodenvir shows promise, but sponsor exits
Early trials indicate the drug can prevent dengue infections, yet its development stalls as Johnson & Johnson abandons dengue antiviral work, leaving a potential breakthrough without a sponsor as the disease spreads.
An antiviral pill for dengue, mosnodenvir, has produced the first clear evidence that a drug can prevent infection in humans, according to early results released this month. Researchers say the high-dose regimen blocked infection in a deliberate exposure study, but the pharmaceutical company that developed the drug, Johnson & Johnson, has withdrawn from dengue antiviral work, leaving the drug without a sponsor as dengue spreads to new regions.
In a series of controlled studies, researchers conducted what is known as a dengue challenge trial, where volunteers are exposed to a weakened dengue virus after taking the medication. Over the past three years, 31 volunteers in Baltimore and Vermont agreed to take mosnodenvir for several days and then be exposed to the virus. Among those who received the highest dose, 6 out of 10 did not develop an infection at all. The other participants who did become infected had significantly lower levels of virus in their blood and milder symptoms than those given a placebo, in which everyone developed infection. At lower doses, the drug delayed infection but did not prevent it—a clear signal that the higher dose was doing something real. "It’s one of the most beautiful dose–response results I’ve seen," said Anna Durbin, the Johns Hopkins researcher who led the study.
In 2023, J&J also launched a broader field trial across more than 30 sites in South America and Asia to test whether mosnodenvir could protect people in the same household who are at high risk of being bitten by the same mosquitoes. Among 265 people who received the highest dose, not a single person developed symptomatic dengue, while 60 percent of those in the placebo group did. (This data hasn’t been formally peer‑reviewed yet, but it’s publicly posted.) For Neelika Malavige, a prominent dengue researcher, the results are a milestone in a field that has struggled for decades to find an antiviral. "The dengue community may be closer than ever to a long‑awaited treatment," she wrote in a commentary accompanying the paper.
Image: dengue research image 1
But there are caveats. The trial showed mosnodenvir can prevent infection, which is not the same as treating someone who is already sick. Public health needs a drug that can halt disease progression after exposure, or after symptoms begin, to prevent severe outcomes like vascular leakage or organ failure. Dengue viruses can overwhelm the body quickly, and the window for effective antiviral treatment is narrow. Researchers emphasize that a drug with both preventive and therapeutic potential would be ideal, but timing remains a critical factor.
Johnson & Johnson’s exit from dengue antiviral development is not an isolated decision; it mirrors a broader shift in the pharmaceutical industry away from infectious diseases toward cancer, obesity, and autoimmune disorders. After announcing a strategic reprioritization last year, J&J transferred mosnodenvir back to KU Leuven, the Belgian university where the drug was discovered before licensing it to J&J. The Wellcome Trust is supporting efforts to find new partners and funding to carry the program forward. KU Leuven and its partners warn that turning a breakthrough into a marketable therapy will require different funding and collaboration models to address the mismatch between need and what the market funds.
In the meantime, other dengue drug candidates are moving along. Swiss drug maker Novartis is testing a separate antiviral in phase 2, and the Serum Institute in India is evaluating a monoclonal antibody. The global health community faces a familiar tension: drug development is expensive and uncertain, and the people who bear the greatest burden of dengue—in low- and middle-income countries—are the least able to pay for breakthrough therapies. Experts say the only way forward is a mix of multiple drugs and strategies, including preventive measures like vaccines, bed nets, and public awareness campaigns to drain standing water.
The dengue virus is on the move. Climate models project that by 2080 nearly 60 percent of the world’s population could live in areas where dengue transmission is possible, expanding far beyond traditional tropical regions. In recent years, cases have risen in southern Europe and the United States, including locally acquired infections in areas previously thought to be low risk. The public health tools currently used to prevent infections—vaccines, vector control, and community education—have limited reach and impact. A drug that could be given at first signs of illness or immediately after exposure would change the landscape of dengue care, but turning mosnodenvir into a widely accessible treatment depends on securing sponsorship and funding for continued development and pragmatic clinical trials.
Ultimately, experts say, the key to defeating dengue lies in a combination of science, funding, and global health policy. Drug developers may be moving away from dengue, but the need remains urgent as climate change, population growth, and urbanization create new frontiers for the virus. The question now is whether another sponsor will step forward to carry mosnodenvir through the next phase of testing, and whether a multi‑drug strategy could finally deliver a reliable antiviral option for people who fall ill with dengue.