H5N1 avian influenza, often called bird flu, was first identified in the United States in 2014. Since then, the virus has moved beyond wild birds, spreading into farm animals and eventually infecting people. More than 70 human cases have been reported in the U.S. since 2022, including two deaths. Because the virus is still circulating widely among animals, scientists warn that it has ongoing chances to adapt in ways that could allow it to spread more easily between humans, raising concerns about a future pandemic. To reduce the risk of widespread transmission, researchers at Washington University School of Medicine in St. Louis developed a vaccine delivered through the nose rather than by injection. When tested in hamsters and mice, the intranasal vaccine triggered strong immune responses and prevented infection after exposure to H5N1. The team also addressed a key challenge facing bird flu vaccines. Immunity from prior seasonal flu infections or vaccinations can sometimes weaken responses to new flu vaccines. In this case, researchers found that the nasal vaccine remained effective even in animals with existing flu immunity. The findings were published Jan. 30 in Cell Reports Medicine. "This particular version of bird flu has been around for some time,...