Researchers at Washington University School of Medicine in St. Louis have developed a groundbreaking nasal vaccine aimed at minimizing the risk of widespread H5N1 bird flu transmission. This innovative approach, which bypasses traditional injection methods, has demonstrated remarkable immune responses in tests conducted on hamsters and mice, effectively preventing infection after exposure to the virus.
The research team tackled a significant challenge in the field of bird flu vaccines: the potential weakening of immune responses due to prior seasonal flu infections or vaccinations. Remarkably, the nasal vaccine maintained its efficacy even in subjects with existing flu immunity.
The findings were published in the journal Cell Reports Medicine on January 30. "This variant of bird flu has been present for some time, but the unexpected transmission to dairy cows in the United States underscores the need for preparedness against potential pandemics," stated Jacco Boon, PhD, a professor in the WashU Medicine John T. Milliken Department of Medicine and co-senior author of the study. "Our nasal vaccine is designed to protect against upper respiratory infections as well as severe disease, offering enhanced protection by preventing infection in the first place."
Advancements in Bird Flu Vaccine Technology
While a bird flu vaccine exists, it is based on older virus strains and may not effectively combat current H5N1 variants. To create a more effective solution, Boon and his team utilized nasal vaccine technology previously developed at WashU Medicine by co-authors Michael S. Diamond, MD, PhD, and David T. Curiel, MD, PhD.
A COVID-19 vaccine utilizing this same platform has been available in India since 2022 and has received approval for clinical trials in the U.S. last year.
Tailoring Immune Responses to the Virus
For a vaccine to be effective, the immune system must swiftly recognize the targeted virus. To achieve this, Boon and co-author Eva-Maria Strauch, PhD, selected proteins from H5N1 strains known to infect humans, engineering an optimized antigen that triggers an immune response.
This antigen was incorporated into a harmless, non-replicating adenovirus, serving as the vaccine's delivery mechanism. This antigen design and adenovirus delivery method closely mirrors that of the COVID-19 nasal vaccine.
Exceptional Protection in Animal Studies
In trials with hamsters and mice, the nasal vaccine provided nearly complete protection against H5N1 infection. In contrast, traditional seasonal flu vaccines offered minimal defense against bird flu. The nasal spray vaccine outperformed the same vaccine delivered via traditional intramuscular injection in both animal models.
Notably, the vaccine retained high effectiveness even when administered at lower doses followed by high virus exposure.
Preventing Infection in the Nose and Lungs
The nasal delivery method elicited strong immune responses throughout the body, particularly in the nasal passages and respiratory tract. Boon emphasized that this approach is advantageous over injected vaccines, as it provides enhanced protection in the nose and lungs, likely reducing severe illness and transmission risk.
"Our nasal vaccine delivery system, developed and tested at WashU Medicine, can prevent H5N1 from establishing infection in the nose and lungs," stated Diamond, co-senior author of the study. "By targeting the upper airway directly, we can disrupt the cycle of infection and transmission, which is critical for controlling the spread of H5N1 and other respiratory viruses."
Further experiments investigated whether prior flu immunity would affect the H5N1 vaccine's performance. The researchers found that the nasal vaccine continued to deliver strong protection, even in subjects with previous flu exposure, a vital consideration for real-world application.
Future Directions for the Nasal Vaccine
The research team is planning additional studies involving animals and organoids that simulate human immune tissue. They are also developing updated versions of the vaccine to minimize the impact of prior seasonal flu immunity and enhance antiviral responses.
This research was supported by the Cooperative Center for Human Immunology and the Center for Research on Structural Biology of Infectious Diseases.
