January 30, 2025, US researchers at the National Institute of Allergy and Infectious disease released the results of their preclinical trial of H5N1 neutralizing antibodies in Science. This could be the first sign of an effective H5N1 ab treatment.
Immunology researchers racing to find a treatment for bovine bird flu discovered that pre-exposure prophylaxis of macaque monkeys with a broadly neutralizing antibody developed against Type A Influenza stops the monkeys from falling ill. This finding will be welcome news for healthcare workers anxious to avoid a repeat of the COVID-19 disaster which saw in hospitals in crisis as doctors and nurses got sick.
Following their success in preventing severe illness, scientists hope that this H5N1 ab treatment could be given to vulnerable populations up to eight weeks before likely exposure to the flu saying, ‘we anticipate that protection from unforeseen pandemic influenza A viruses is achievable.’
Like COVID-19, this novel highly pathogenic strain of H5N1 is new to human immune systems. Just different enough from regular flu, this virus won’t be stopped by seasonal flu vaccines and we don’t carry long-term immunity based on previous challenges.
The researchers led by Masaru Kanekiyo, D.V.M, Ph.D., at the University of Pittsburgh used an existing broadly neutralizing antibody (bnAb) developed by a subsidiary of pharma company Astra Zeneca. They tested its ability to prevent severe illness and fatality in monkeys infected with the new H5N1 strain. Different doses of antibody were given to sets of monkeys, ranging from 0 mg (control) to 30 mg/kg (maximum).
Three days later the scientists exposed the macaques to aerosolized highly pathogenic H5N1 to cause a typical flu infection. Monkeys in the 0 mg of antibody control group got very sick with flu and some died. Monkeys who received a dose of the antibody, on the other hand, did not get sick or die. The antibody had a dose responsive effect, the more antibody the monkey had, the better it worked. At 10 mg/kg, the macaques had no respiratory symptoms. The antibody was still detectable up to two months after monkeys received their dose.
This study is in the preclinical stages, we may be waiting some time to see occupational health departments making this available to healthcare workers. Before it can hit the pharmacy, this treatment needs to go through clinical trials and be approved by medical regulatory bodies. The antibody was approved for fast track FDA consideration in 2016, and has been making its way through phase II clinical trials for regular flu since 2018.
This drug is a monoclonal antibody designed to bind to a chunk of the haemagglutinin protein on the outside of the virus. The piece of protein to which the antibody sticks, is very resistant to mutation. This means that the difference between this specific piece of protein in different strains within the Type A subgroup of flu virus is very small. Basically, if it changes too much, the haemagglutinin protein won’t be able to help the virus get into a cell and infect it. The immunologists are taking advantage of this feature to attack the virus blocking its ability to infect cells.
Sources
Kanekiyo M, Gillespie RA, Cooper K, et al. Pre-exposure antibody prophylaxis protects macaques from severe influenza. Science. 2025;387 (6733):534–541. doi:10.1126/science.ado6481
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Single dose of broadly neutralizing antibody protects macaques from H5N1 influenza. National Institutes of Health (NIH). February 10, 2025. Accessed February 18, 2025. https://www.nih.gov/news-events/news-releases/single-dose-broadly-neutralizing-antibody-protects-macaques-h5n1-influenza
MedImmune receives fast track designation in the US for MEDI8852 for treatment of patients hospitalized with influenza A. March 7, 2016. Accessed February 18, 2025. https://www.astrazeneca.com/media-centre/press-releases/2016/Medimmune-receives-fast-track-designation-in-the-US-for-MEDI8852-for-treatment-of-patients-hospitalised-with-influenza-A-07032016.html
