One possible scenario for spillover into the population: a raw-milk drinker or a farmworker gets infected with this strain of H5N1 that’s moving among cattle and also gets co-infected with a human-adapted strain of influenza. In such a situation viruses can swap genes in a process called reassortment. A major fear about H5N1 has always been that it might do this. H5N1 has shown it can easily move from one species to another, acquiring new genetic material in the process.
Or someone catches H5N1 from a cow or its raw milk, and—perhaps through an immune deficiency—they develop a long-lasting infection that allows the virus to mutate in their body. “There absolutely is a risk here,” says Richard Webby, an expert in animal and human viruses who works at St. Jude Children’s Research Hospital in Memphis.
Here’s what it takes for a virus to start a human pandemic: it must acquire the ability to infect people easily; it must then pass easily from person to person; and it must cause significant illness.
“The more it spreads within mammals, that gives it more chances to mutate. As it mutates, as it changes, there is a greater chance it can infect humans. If it gains the ability to spread efficiently from person to person, then it would be hard to stop,” says Nita Madhav, a former U.S. Centers for Disease Control and Prevention researcher who is now senior director of epidemiology and modeling at Ginkgo Biosecurity.
This can happen fast. “We’ve all seen how a virus can spread around the globe before public health has even had a chance to get its shoes on,” Nirav Shah, principal deputy director at the CDC, said at a Council on Foreign Relations briefing in May. It only took three years for COVID to kill seven million people.
So far, the H5N1 virus has infected three dairy farm workers, according to the CDC. Those are the known cases. The CDC has not even begun to jump through the hoops needed to force inspections and testing—and any such moves would almost certainly result in prolonged legal battles with both the dairy industry and some states.
Source: H5N1 Bird Flu Isn’t a Human Pandemic—Yet | Scientific American











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