Nasal spray vaccine protects against bird flu in mice

Novel H5N1 vaccine confers robust protection regardless of prior seasonal flu immunity

WashU Medicine researchers showed that an experimental bird flu vaccine provides strong protection in mice, even in animals previously vaccinated against seasonal flu. Delivered as a nasal spray, the vaccine guards the nose and upper airways better than a traditional shot, and it can be manufactured without eggs, making it more practical to scale up during an outbreak. (Credit: Getty Images)

WashU Medicine researchers led by Jacco Boon, PhD, a professor in the John T. Milliken Department of Medicine, report that an experimental bird flu vaccine provides strong immune protection in mice, including in animals previously vaccinated against seasonal flu. Because pre-existing immunity from prior seasonal influenza infection or vaccination could diminish the efficacy of H5N1 vaccines, showing that the new vaccine succeeds alongside existing immunity is a crucial milestone.

Photo of Jacco Boon, PhD in white doctor's coat — Boon

Building on Boon’s prior work on bird flu vaccines delivered nasally, the study, published online July 10 in npj Vaccines and funded by Novavax Inc., shows that delivering the vaccine to the nose offers better protection against infection in the nose and upper airways than a traditional injection.

The novel vaccine pairs a key protein on the surface of the H5N1 bird flu virus with an immune-boosting ingredient used in some newer COVID-19 and malaria vaccines, to prime the immune system to attack this protein. In mice already vaccinated against seasonal flu, a single dose of the H5N1 vaccine generated strong virus-fighting antibodies against the strain of bird flu identified in the 2024 U.S. outbreak, which heavily impacted the poultry and dairy industries and caused two human deaths. In contrast, mice with no prior flu exposure required two doses of the new vaccine to achieve the same level of protection.

Unlike many existing vaccines, this vaccine does not rely on eggs for production, making it more practical to manufacture large quantities during an outbreak. Future testing will determine if it also blocks disease transmission.

Kelly Pyles, Tamarand L. Darling, Lin-Chen Huang, Mimi Guebre-Xabier, Melinda Hersey, Ann M. Greene, Nita Patel, Gale Smith & Adrianus C. M. Boon. Intranasal and intramuscular H5-Matrix-M nanoparticle vaccines protects against highly pathogenic H5N1 influenza virus in mice. npj Vaccines (2026). https://doi.org/10.1038/s41541-026-01523-8.