Headlines are flying after the Department of Agriculture confirmed that the H5N1 bird flu virus has infected dairy cows around the country. Tests have detected the virus among cattle in nine states, mainly in Texas and New Mexico, and most recently in Colorado, said Nirav Shah, principal deputy director at the Centers for Disease Control and Prevention, at a May 1 event held by the Council on Foreign Relations.

A menagerie of other animals have been infected by H5N1, and at least one person in Texas. But what scientists fear most is if the virus were to spread efficiently from person to person. That hasn’t happened and might not. Shah said the CDC considers the H5N1 outbreak “a low risk to the general public at this time.”

Viruses evolve and outbreaks can shift quickly. “As with any major outbreak, this is moving at the speed of a bullet train,” Shah said. “What we’ll be talking about is a snapshot of that fast-moving train.” What he means is that what’s known about the H5N1 bird flu today will undoubtedly change.

With that in mind, KFF Health News explains what you need to know now.

Q: Who gets the bird flu?

Mainly birds. Over the past few years, however, the H5N1 bird flu virus has increasingly jumped from birds into mammals around the world. The growing list of more than 50 species includes seals, goats, skunks, cats, and wild bush dogs at a zoo in the United Kingdom. At least 24,000 sea lions died in outbreaks of H5N1 bird flu in South America last year.

What makes the current outbreak in cattle unusual is that it’s spreading rapidly from cow to cow, whereas the other cases — except for the sea lion infections — appear limited. Researchers know this because genetic sequences of the H5N1 viruses drawn from cattle this year were nearly identical to one another.

The cattle outbreak is also concerning because the country has been caught off guard. Researchers examining the virus’s genomes suggest it originally spilled over from birds into cows late last year in Texas, and has since spread among many more cows than have been tested. “Our analyses show this has been circulating in cows for four months or so, under our noses,” said Michael Worobey, an evolutionary biologist at the University of Arizona in Tucson.

Q: Is this the start of the next pandemic?

Not yet. But it’s a thought worth considering because a bird flu pandemic would be a nightmare. More than half of people infected by older strains of H5N1 bird flu viruses from 2003 to 2016 died. Even if death rates turn out to be less severe for the H5N1 strain currently circulating in cattle, repercussions could involve loads of sick people and hospitals too overwhelmed to handle other medical emergencies.

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