As the magnitude of the bird flu outbreak in cattle becomes clearer, so does the need to quickly get a firmer grip on some basic facts. Namely, how far this H5N1 virus has spread, how it is spreading, and where this situation is likely to go next. The Covid-weary public also wants to know whether humans are at risk.
Public agencies must move faster and collaborate more efficiently to answer some of those unknowns. After all, this is a pathogen that has loomed large in the minds of infectious disease experts for its potential to cause a deadly human pandemic. “It’s fair to say for every question we’ve had answered in the last month, we have 10 to 15 new questions,” says Michael Osterholm, director of the Center for Infectious Disease Research and Policy in Minnesota.
Among the most essential: Just how widespread is this outbreak?
The seriousness of the situation escalated after scientists found viral fragments in milk on grocery store shelves—including in states that had not reported infected herds. The Food and Drug Administration eventually said it had detected H5N1 fragments in one out of every five of the commercial milk samples it tested.
That suggests the virus has been circulating in cows longer and more easily than anyone realized. Genetic sleuths have traced the outbreak back to a likely spillover event in late 2023, when a wild bird may have infected a cow on a farm.