New study suggests seasonal flu vaccines may reduce severity of H5N1 bird flu infections

TAMPA, Fla. (April 28, 2026) -- As potentially deadly avian influenza (H5N1) continues its global spread, moving from birds into mammals and in rare cases into humans, scientists are confronting a difficult reality. If a human pandemic emerges, vaccines designed specifically to protect people against H5N1 may not be ready in time.

New international research led by National Taiwan University, in collaboration with the University of South Florida, suggests that part of the answer may already exist.

In a recent study published in Emerging Microbes & Infections, researchers found that seasonal influenza vaccines in routine global use may significantly reduce the risk of death from H5N1 infection. The findings highlight an important implication for pandemic preparedness, suggesting that readily available tools may offer protection while the world races to develop more targeted solutions.

The Taiwan-U.S. research team performed a systematic review and analysis of nearly two decades of experimental data from 35 controlled studies. Seasonal flu vaccines that included a specific component, neuraminidase N1, reduced H5N1-related mortality by approximately 73 percent in vaccinated animals compared with unvaccinated animals.

That level of protection was comparable to some H5N1-specific vaccines that failed to generate strong immune responses and was only modestly lower than those that did.

In contrast, seasonal vaccines lacking the N1 component showed little to no protective effect, underscoring how specific elements of existing vaccines may play an outsized role in defending against emerging threats.

“This work suggests that we may be underestimating the broader protective value of seasonal influenza vaccines,” said Chi-Tai Fang, MD, PhD, professor of infectious diseases epidemiology at National Taiwan University and National Taiwan University Hospital and senior author of the study. “While they are not designed to target H5N1, certain components appear to activate immune responses that can reduce the severity of infection. In a real-world setting, that kind of partial protection could translate into lives saved while more specific vaccines are being developed and distributed.”

Sten Vermund, MD, PhD, dean of the USF Health College of Public Health, chief medical officer of the Global Virus Network and a co-author, said the findings highlight an important opportunity for pandemic preparedness.

“In a pandemic scenario, timing is everything,” Vermund said. “We often face a critical gap between the emergence of a new virus and the availability of a targeted vaccine. Our findings suggest that seasonal flu vaccination, something already widely available, could help reduce severe outcomes during that window. That is a meaningful advantage when every week matters.”

The study also revealed something unexpected. The seasonal vaccines did not produce detectable antibodies against H5N1 using standard tests. Instead, the protection appears to come from more complex immune mechanisms likely involving cross-reactive cellular responses that are not captured by traditional measures of immunity, suggesting protection may exist even when it is not detectable through standard laboratory markers.

The findings arrive at a critical moment, as H5N1 continues to spread among mammals while limited vaccine are available globally. This leaves health systems vulnerable in the early stages of an outbreak. While not a substitute for targeted vaccines, extensive adoption of seasonal flu vaccines could buy time by reducing deaths, easing strain on health systems and slowing the impact of a rapidly spreading virus.

The researchers caution that the findings are based on animal models and must be validated in humans, but they also point to an important next step in understanding how existing immunity built through routine vaccination may shape responses to emerging infectious diseases.

About the University of South Florida

The University of South Florida is a top-ranked research university serving approximately 50,000 students from across the globe at campuses in Tampa, St. Petersburg, Sarasota-Manatee and USF Health. In 2025, U.S. News & World Report recognized USF with its highest overall ranking in university history, as a top 50 public university for the seventh consecutive year and as one of the top 15 best values among all public universities in the nation. U.S. News also ranks the USF Health Morsani College of Medicine in the highest tier, placing it as one of the top 16 medical schools in the nation and inside the top 10 among public universities. USF is a member of the Association of American Universities (AAU), a group that includes only the top 3% of universities in the U.S. With an all-time high of $750 million in research funding in 2025 and as a top 20 public university for producing U.S. patents, USF uses innovation to transform lives and shape a better future. The university generates an annual economic impact of nearly $10 billion for the state of Florida. USF’s Division I athletics teams compete in the American Conference. Learn more at www.usf.edu.