Researchers at Washington University report that an intranasal H5N1 vaccine produced a strong immune response and near-complete protection against multiple strains in rodents. Nasal vaccines generate mucosal immunity in the nose and airways, which can block infection and reduce transmission more effectively than injected shots. The study appears in Cell Reports, but the vaccine remains preclinical and will require extensive human trials before it could be deployed.
Nasal-Spray Vaccine Shows Near-Complete Protection Against H5N1 in Early Trials — Could It Curb The Next Pandemic?
Most of the H5N1 vaccines already stockpiled were developed to match older virus strains - Simon Townsley
Researchers at Washington University School of Medicine report encouraging early results for a nasal-spray vaccine targeting H5N1 bird flu, showing a strong immune response and near-complete protection in rodents. The findings, published in the peer-reviewed journal Cell Reports, highlight the potential of intranasal vaccines to block infection at the site respiratory viruses first enter the body.
In the preclinical study, scientists administered the H5N1 vaccine as a fine spray into each nostril of rodents. The intranasal formulation produced what the team described as a "strong immune response" and provided broad protection against multiple H5N1 strains — outperforming the same formulation given by injection in measures of overall immunity.
Why Nasal Vaccines Matter
Traditional injected flu vaccines are effective at reducing severe disease, but vaccinated people can still become infected and transmit the virus: studies suggest a 40–60% chance of asymptomatic infection and onward spread even after vaccination. Nasal vaccines stimulate mucosal immunity in the nose and airways, the primary sites of infection and replication for respiratory viruses. By blocking the virus at these entry points, intranasal vaccines can both prevent illness and reduce transmission.
“Delivering vaccines directly to the upper airway — where you most need protection from respiratory infection — could disrupt the cycle of infection and transmission. That’s crucial to slowing the spread of infection for H5N1,” said Dr Michael Diamond, Professor of Molecular Microbiology at Washington University and a co-author of the study.
Context And Risks
The development comes amid a surge of H5N1 activity in animals worldwide. Since October alone, more than nine million birds have been culled following farm outbreaks in the United States, Canada and Europe. The virus has also been found in U.S. dairy cattle and was detected in European cows in the Netherlands for the first time.
Human exposure is rising: at least 70 people in the United States have been infected with H5N1 since 2024, mostly after close contact with infected animals, and one of those cases was fatal. Historically, H5N1 infections have been especially severe — of roughly 900 known human cases since the late 1990s, nearly half have died.
Many countries have stockpiled H5N1 vaccines, but most of those were developed to match older strains from the mid-2000s and may be poorly matched to rapidly evolving variants circulating since 2020. Some estimates put the effectiveness of older stockpiled vaccines against current strains as low as 45%.
Limits And Next Steps
While the rodent results are promising, the vaccine is still in an early preclinical stage. Extensive testing in humans, including multiple clinical trial phases, is required to confirm safety, dosing, durability of protection and effectiveness against circulating human-adapted strains. That development pathway typically takes several years.
In short, intranasal H5N1 vaccines could become a valuable tool for blocking infection and transmission, but the science must progress through rigorous human trials before any public-health deployment is possible.
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