SCIENCE.ORG – If the world finds itself amid a flu pandemic in a few months, it won’t be a big surprise.
Birds have been spreading a new clade of the H5N1 avian influenza virus, 2.3.4.4b, around the world since 2021.
That virus spilled over to cattle in Texas about a year ago and spread to hundreds of farms across the United States since. There have been dozens of human infections in North America.
And in some of those cases the virus has shown exactly the kinds of mutations known to make it better suited to infect human cells and replicate in them.
No clear human-to-human transmission of H5N1 has been documented yet, but “this feels the closest to an H5 pandemic that I’ve seen,” says Louise Moncla, a virologist at the University of Pennsylvania.
“If H5 is ever going to be a pandemic, it’s going to be now,” adds Seema Lakdawala, a flu researcher at Emory University.
Others are more sanguine, noting that similarly menacing avian flu viruses, such as one called H7N9, have petered out in the past …
So why hasn’t H5N1 touched off a pandemic yet?
One simple answer is that the virus may just need more time to hit the right combination of mutations.
The high mutation rate of influenza viruses should tip the odds in H5N1’s favor: “My rule of thumb is that one in 4000 [virus] particles will have a mutation at the amino acid that you are interested in,” Paulson says.
Indeed, one polymerase mutation the virus likely needs, dubbed 627K because it leads to the amino acid lysine (K) at position 627 of the protein, has been found several times in strains infecting mammals but also in virus isolated from the first human case associated with the U.S. outbreak in dairy cows …
