Nasal spray vaccine prevents infection from highly pathogenic H5N1 virus

A new nasal vaccine shows significant promise in protecting against the H5N1 avian influenza virus, commonly known as bird flu. Developed by researchers at Washington University School of Medicine in St. Louis, the vaccine demonstrated a strong immune response and prevented infections in animal models.

The Rising Threat of H5N1

Since its initial detection in the U.S. in 2014, H5N1 has spread from wild birds to farm animals and, increasingly, to humans. As of data available January 30, 2024, the virus has caused more than 70 human cases in the U.S. since 2022, including two fatalities. The continued circulation of H5N1 among animals raises concerns about its potential to mutate and spread more easily between people, potentially triggering a pandemic.

Did You Know? The unexpected jump of H5N1 into dairy cows in the United States signaled a need for increased pandemic preparedness.

A Novel Approach to Vaccination

Existing bird flu vaccines are based on older viral strains and may not be effective against current variants. The WashU Medicine team leveraged existing nasal vaccine technology, previously used in a COVID-19 vaccine available in India and approved for U.S. clinical trials, to create a new vaccine. This technology focuses on delivering the vaccine directly to the nose and upper airway.

The vaccine’s antigen—the component that triggers an immune response—was carefully designed using proteins from currently circulating H5N1 viruses. These proteins were then delivered via a harmless, non-replicating adenovirus. This method is similar to the approach used in the COVID-19 nasal vaccine.

Testing in hamsters and mice showed near-complete protection against infection with the nasal vaccine. Current seasonal influenza vaccines offered little protection against H5N1 in comparison. Importantly, the nasal spray outperformed traditional intramuscular immunization in both animal models, even at low doses and high exposure levels.

Expert Insight: Delivering a vaccine directly to the upper airway, where respiratory infections first take hold, could be a crucial strategy for not only preventing severe illness but also disrupting the spread of infection.

The nasal delivery method generated a strong immune response throughout the body, with a particularly robust effect in the nose and respiratory tract. This targeted approach is believed to offer better protection against transmission, as it addresses infection at its source.

Overcoming Pre-Existing Immunity

Researchers also investigated whether prior exposure to influenza viruses or vaccines would diminish the effectiveness of the new H5N1 vaccine. They found that the nasal vaccine remained highly effective even in animals with pre-existing immunity, a critical advantage for widespread use since most people have some level of prior flu exposure.

The research team plans to conduct further studies in animals and human immune tissue models. They also aim to develop vaccine versions that further minimize the impact of prior seasonal influenza exposure and enhance antiviral responses.

Frequently Asked Questions

What is an antigen?

An antigen is the part of a pathogen—like a virus—that the immune system recognizes and reacts to.

How is this vaccine different from a traditional flu shot?

This vaccine is delivered as a nasal spray, directly to the upper airway, rather than as an injection into the arm.

Does prior flu vaccination affect the effectiveness of this new vaccine?

No, the researchers found that the nasal vaccine provided strong protection even in animals with pre-existing immunity from prior flu vaccines or infections.

Will this vaccine be widely available? It remains to be seen what further testing and approvals will be required before this vaccine could be made available to the public.