Nature Older populations might be more protected than younger ones because of exposure to ‘matched’ strains during childhood, but an H5N1 pandemic is likely to take a major toll all the same.
As the H5N1 bird-flu virus spreads relentlessly in animals around the world, researchers seeking to understand how a human H5N1 pandemic might unfold have turned to a rich source of clues: data on the immune system’s response to influenza.
Such information provides hints about who could be most vulnerable in an H5N1 pandemic. Previous research also suggests that, in a confrontation with the virus, our immune systems would not be starting from scratch — thanks to previous infections with, and vaccinations against, other forms of flu. But this immunity is unlikely to prevent H5N1 from inflicting serious damage to global health, if a pandemic were to begin.
From feathers to fur
The H5N1 strain now running rampant began as a bird pathogen before branching out to mammals. Classified as a ‘highly pathogenic’ virus for its lethality in birds, it has killed millions of domestic and wild birds around the world since it first emerged in 1996.1 It has also spread to a growing list of mammal species, including seals and foxes, and has caused more than 460 human deaths since 2003.
So far, the virus has not gained the ability to spread effectively between people, which has kept the potential for a pandemic at bay. But its repeated jumps from birds to mammals and evidence of transmission among mammals, such as elephant seals (Mirounga leonina)2, have alarmed researchers, who warn that the virus is gaining opportunities to become adept at spreading easily between people.