“To be honest, there’s probably many people around the country that have this virus in their freezer, with a duck that they’ve shot.”
The same goes for people, to some extent. While the U.S. is very good at sequencing flu cases in humans to see which versions of the virus cause illness, we know less about people who encounter viruses like H5N1 but feel fine. “To be honest, there’s probably many people around the country that have this virus in their freezer, with a duck that they’ve shot, so there is a lot of human exposure going on,” Webby said. “How much actual infection, we don’t actually have a good feel for.” Monitoring exposures among humans—checking blood samples to see how many people have encountered the virus—could give us an idea of whether, and to what extent, we’ve already been infected by H5N1. “I do think that there is a potential that we are missing some infections because they’re asymptomatic or low symptomatic,” Lakdawala said.
But the very low rate of reported infections among people—in this outbreak, fewer than 10 people around the world have tested positive for H5N1, with one severe case in a child in Ecuador—is a sign that so far, the virus isn’t wreaking widespread havoc on us. “If there was an uptick in severe disease, flu-like illness, particularly offseason at a location where there is known activity of this virus, then that would ring warning bells for sure,” Webby said.
Another telling sign would be the spread of H5N1 from mammals to people, and, even more alarmingly, from people to people. So far, the only known cases have been among people with direct, usually prolonged, contact with infected birds. “We haven’t had any mammalian-to-human transmission events yet, so I think I’d be most concerned if we started to hear that,” Lakdawala said. And “until we hear about more human infections, I’m less concerned about human-to-human transmission—but that doesn’t mean that the risk is negligible.”