New nasal vaccine shows strong protection against H5N1 bird flu

Since 2014, H5N1 avian influenza, commonly known as bird flu, has expanded its reach beyond wild birds, infecting farm animals and, since 2022, more than 70 people in the United States, including two fatalities. The continued circulation of the virus among animals raises concerns among scientists that it could adapt to spread more easily between humans, potentially leading to a pandemic.

A New Approach to Bird Flu Protection

Researchers at Washington University School of Medicine in St. Louis have developed a nasal vaccine designed to combat the spread of H5N1. Testing in rodents—hamsters and mice—showed the vaccine triggered strong immune responses and prevented infection after exposure to the virus. This vaccine differs from traditional methods by being delivered through the nose, rather than by injection.

A key challenge in bird flu vaccine development is that prior immunity from seasonal flu vaccinations can sometimes reduce the effectiveness of new vaccines. However, the researchers found that this nasal vaccine remained effective even in animals with existing flu immunity.

Designing a Targeted Immune Response

The vaccine’s design focused on selecting proteins from H5N1 strains known to infect humans. Researchers, including Eva-Maria Strauch, PhD, an associate professor of medicine, engineered an optimized antigen—the part of the virus that triggers an immune response—using shared features of these viral proteins. This antigen was then delivered using a harmless, non-replicating adenovirus.

According to Jacco Boon, PhD, a professor in the WashU Medicine John T. Milliken Department of Medicine and co-senior author of the study, “Our vaccine to the nose and upper airway — not the shot-in-the-arm vaccine people are used to — can protect against upper respiratory infection as well as severe disease. This could provide better protection against transmission because it protects against infection in the first place.”

Animal studies demonstrated near-complete protection against H5N1 infection with the nasal vaccine. The nasal spray also provided stronger protection than the same vaccine delivered via traditional injection. The vaccine remained highly effective even at low doses and with high levels of virus exposure.

Blocking Infection at the Source

The nasal delivery method produced strong immune responses throughout the body, particularly in the nasal passages and respiratory tract. Michael S. Diamond, MD, PhD, the Herbert S. Gasser Professor of Medicine, explained that delivering the vaccine directly to the upper airway could disrupt the cycle of infection and transmission.

Frequently Asked Questions

What is H5N1 avian influenza?

H5N1 avian influenza, or bird flu, is a virus that first appeared in the U.S. In 2014 and has since spread from wild birds to farm animals and people. Since 2022, more than 70 human cases have been reported in the U.S., including two deaths.

How does this new vaccine differ from existing bird flu vaccines?

This vaccine is delivered through the nose, rather than by injection, and uses a new antigen design. It also remains effective even in animals with prior immunity from seasonal flu vaccinations, which can sometimes weaken the response to other flu vaccines.

What are the next steps for this vaccine?

The research team plans to conduct further studies in animals and in organoids that model human immune tissue. They are also working on updated versions of the vaccine to further reduce the influence of prior seasonal flu immunity and enhance antiviral responses.

What role might new vaccine technologies play in preparing for future pandemics?