The antibody focuses on a consistent area of the bird flu virus, which enables the immune defense to endure against emerging strains and provides prolonged protection against the rapidly spreading airborne disease.
Researchers from the University of Pittsburgh and the NIH Vaccine Research Center have announced today in Science that an antibody-based immune therapy can prevent severe H5N1 avian flu in monkeys.
This broadly neutralizing antibody targets a stable part of the bird flu virus, making it less likely to lose effectiveness compared to antibodies directed at the virus’s more variable features. This characteristic ensures that the immune defense can adapt to any newly arising viral variants, similar to the SARS-CoV-2 mutations observed during the COVID-19 pandemic, thus offering long-lasting defense against a globally transmissible airborne illness.
“Such preventive measures can play a critical role in managing infection outbreaks and mitigating a potential bird flu pandemic,” stated co-corresponding author Douglas Reed, Ph.D., an associate professor of immunology at Pitt’s School of Medicine and the Center for Vaccine Research. “Our testing showed that the antibody worked exceptionally well. It could serve as a preventive treatment for severe illness in at-risk groups, and it helped us establish the threshold levels of antibodies needed in the bloodstream, which would be beneficial for evaluating the immune response provided by a universal flu vaccine.”
As of January 2025, only one reported case of H5N1 infection has resulted in death in the United States. However, the World Health Organization has documented over 950 global cases since 1997, with more than half resulting in fatalities. Concerns regarding the potential for broader transmission are growing. H5N1 has been spreading among livestock in the U.S. and has also transmitted from wild birds to mammals worldwide, including sea lions in South America and mink in Europe. Genetic analysis of two human samples in North America indicates that the virus is progressing in its ability to infect and spread among mammals.
Pitt researchers have long studied the threat of avian flu transmission from animals to humans, developing preventive measures—such as vaccines and protective antibodies—in animal models that closely resemble human physiology. A study published in iScience in 2023 detailed advancements in their aerosol monkey model, which mimics severe H5N1 infection symptoms in humans, including acute respiratory distress syndrome, a serious lung injury arising from bird flu exposure.
One significant challenge in creating a preventive treatment for flu infections is the virus’s quick ability to adapt to new situations, as noted by the researchers. Seasonal flu viruses change rapidly to escape immune responses that have developed over previous years, necessitating annual reformulation of the seasonal flu vaccine to target the dominant strain. Antibodies that focus on the hemagglutinin stalk region, which is preserved across various influenza strains like the H5N1 version studied, bypass this challenge and offer broad neutralizing defense.
“This antibody is aimed at a region that stays constant across different influenza viruses,” explained co-corresponding author Simon Barratt-Boyes, Ph.D., professor of infectious diseases and microbiology at Pitt’s School of Public Health and immunology at Pitt’s School of Medicine. “Think of it as a tree—different species have distinct leaves and branches, but the main trunk appears very similar. Likewise, the stalk region of the bird flu virus is closely aligned with the structure seen in seasonal influenza, which enables stalk-targeting antibodies to deliver universal protection.”
In the latest study, monkeys that received a moderate dose of the broadly neutralizing MEDI8852 antibody were completely shielded against severe illness and mortality. Not only did the study confirm the antibody’s effectiveness in preventing serious health issues, but it also identified the minimum serum concentration necessary for protection, providing crucial data for establishing the protective benchmarks of a potential universal flu vaccine.
This research paves the way for developing medical defenses against future influenza pandemics. Serum levels of MEDI8852 that ensure protection were found to remain stable for 8 to 12 weeks, indicating that early administration could safeguard first responders and caregivers at the onset of an H5N1 outbreak.
Masaru Kanekiyo, Ph.D., from the NIH Vaccine Research Center, also contributed to this research. Other collaborators on this study are affiliated with the NIH Vaccine Research Center, Pitt, UPMC, University of Georgia, and AstraZeneca.
