As concerns around bird flu grow, there may be a silver lining. Scientists from the University of Pittsburgh and the National Institutes of Health’s Vaccine Research Center have published results from a study that show that a prophylactic antibody-based therapy successfully protects monkeys against severe diseases caused by H5N1 avian flu. The details are published in a new Science paper titled, “Pre-exposure antibody prophylaxis protects macaques from severe influenza disease.”
According to the scientists, the broadly neutralizing antibody, called MEDI8852, recognizes a relatively stable region of the bird flu virus. This feature makes it less prone to losing its efficacy than antibodies that target influenza’s more mutation-prone structures. It also ensures that the immune protection provided can withstand the possible emergence of virus variants, and provide lasting protection.
As of January 2025, only one reported case of H5N1 infection in the United States has resulted in death. Worldwide, the World Health Organization has reported over 950 cases globally since 1997 with more than half of them fatal. Besides spreading among cattle, H5N1 cases have also been reported in migratory wild birds and mammals like sea lions, dolphins, and mink. Furthermore, genetic analysis of human samples suggests that the virus is adapting and getting better at spreading the disease in mammals raising new concerns about human-to-human spread.
Pitt researchers have been developing and testing prophylactic interventions including vaccines and protective antibodies in animal models for some time. An important concern about developing prophylactics has to do with viruses’ ability to adapt to new conditions and environments. This is why seasonal flu vaccines must be reformulated yearly to match the dominant strain.
Antibodies that target the hemagglutinin stalk region, which is preserved across different influenza isolates including H5N1, circumvent this challenge. For Simon Barratt-Boyes, PhD, a corresponding author on the study and professor of infectious diseases, microbiology, and immunology at Pitt, it’s helpful to “think about it as a tree—different species have different leaves and crowns, but tree trunks look very much the same. Similarly, the stalk region of the bird flu virus closely resembles the same structure of seasonal influenza, which makes it possible for stalk-targeting antibodies to provide universal protection.”
According to the paper, the researchers pre-treated macaques with a moderate dose of MEDI8852. Besides confirming the antibody’s efficacy in preventing serious adverse health outcomes in the study subjects, the scientists also established a minimum serum concentration required for protection—a useful value for determining the protective threshold of a potential universal flu vaccine. Furthermore, the protective levels of MEDI8852 remained stable in monkey serum for 8 to 12 weeks, suggesting that, if given early, it could protect first responders and caregivers at the beginning of an outbreak.
“This type of prevention can be very useful in controlling infection outbreaks and containing the bird flu pandemic,” said Douglas Reed, PhD, an associate professor of immunology at Pitt’s School of Medicine and the Center for Vaccine Research and one of the corresponding authors on the study. “The antibody could be useful as a prophylactic of severe disease in vulnerable populations, and it also helped us establish the testing threshold for antibody levels in blood, which would be useful for judging the immune protection generated by a universal flu vaccine.”
