Is Bird Flu Gone for Good?
U.S. bird flu infections have declined in both birds and mammals, prompting CDC to shift from weekly to monthly reporting. But is the outbreak really over?
It’s not unusual for wild birds to be infected by influenza viruses.
But the strain of highly pathogenic avian influenza that began causing outbreaks in the U.S. in wild birds and on poultry farms in 2022 has had an unusual trajectory: It has infected humans and a range of other species from farm animals to marine mammals.
The U.S. has recorded only three cases of H5N1 in humans this year—compared with 67 in 2024. But that doesn’t mean we should lower our defenses, says , PhD, MSc, a senior scholar at the and an associate professor in Environmental Health and Engineering. In a Q&A adapted from the of Public Health On Call, Sorrell explains why now is the time to prepare for migratory birds’ return to the U.S., and why we need an “integrated response” to H5N1 that connects data for all affected species.
Can you provide some background on the H5 bird flu and what the current state of the outbreak is?
H5 influenza is a highly pathogenic strain of flu. It is not uncommon for H5 to cause infections in birds, and it’s carried by wild birds on their migratory routes. What’s different about this outbreak is the number of species that this virus has been able to infect and the duration of the outbreak.
and really hasn’t gone away. It’s spread into domestic poultry and a variety of wild bird species. It has affected marine mammals and wild mammals, and now we have had outbreaks in dairy cattle, which is something that was really unexpected before 2024.
Is this a public health emergency? How is it characterized?
For people who are living through it—individuals working on farms, farm owners, people working in the poultry and dairy industries—it’s absolutely an emergency. For the general public, not so much.
CDC hasn’t declared a public health emergency because this virus has not shown the ability to transmit human to human, so the risk for spread at a community level is very low.
If you work on a poultry farm and there’s an outbreak, how do you limit exposure?
The poultry industry has effective standard operating procedures and policies to respond to avian influenza. This particular strain is very lethal to poultry, so it can wipe out a poultry farm, backyard flocks, or a large-scale poultry house very quickly. Typically birds succumb to infection within 48 hours of being exposed and infected.
The ethical response when this strain is detected is to depopulate that farm. This not only contains the outbreak—including the potential spread to other farms and to other species on that farm—but also spares the birds undue pain.
You’ve written recently about a suggestion made by the Health and Human Services and Agriculture secretaries to let the disease spread through flocks. What is the rationale for that?
Robert F. Kennedy Jr. has expressed in different fora that if we let the disease take its course in poultry farms, then we could select for birds that survive infection and then repopulate with those birds that survive. The idea is that those birds may have some resistance to future infections.
, saying that not only is that an unethical way to treat animals during a very lethal contagious infection, but it’s also quite dangerous in terms of potential exposure to other animals.
If you just let the virus spread, not only are you waiting for suffering animals to die, but you’re also essentially creating a virus factory on those farms. The virus continues to replicate, the animals continue to shed that virus, and other species in the environment get exposed.
At some point, those animals are going to have to be removed, and those farms are going to have to be decontaminated, increasing human exposure to the virus. It’s not just the poultry that we have to consider.
It also seems like a recipe for economic disaster. If you let all your chickens die, then you have no chickens.
Yes, but if your response is to cull the flock, then you’re also losing your chickens.
The poultry industry has systems in place for early detection and response, so if you detect and depopulate rapidly, then you can also repopulate your farm quickly. It takes a couple of weeks to raise chickens for meat and a couple of months to raise them for eggs. Chickens reach maturity pretty quickly.
That’s assuming we have still the genetic line in which there is the ability to breed those chickens. If we let the virus spread and we lose those genetic lines, those farms may need to repopulate their farms with poultry that don’t have the same egg and meat production of the chickens killed by the virus. It’s just not something we can predict, so it’s quite a risk. It takes generations of breeding and selection to create those genetic lines.
And this “let it spread” approach selects for surviving one virus. Surviving H5 doesn’t necessarily mean that those chickens would survive exposure to another influenza subtype.
We were keeping very close tabs on bird flu several months ago. Are we still doing that surveillance?
It’s a great question, and it’s an interesting time to be asking it.
Migratory birds have gone south, so we are going to have fewer cases reported right now, both in avian species and dairy cattle. As a result, we’ll likely have less chances of exposure in humans and other mammalian species. We’ve seen cases in South American countries where the birds have migrated. Those birds will come back north, but we do have some time now to plan and prepare.
But as of July 7, , so it will be much harder to track when there’s an uptick in potential exposures. It is less likely that we’ll be able to see it quickly.
And CDC is not tracking animal cases anymore. It used to be that on the same page, you’d see on a weekly basis the number of human cases along with how many cases have been reported in different animal species, and that was all linked to USDA databases. Now CDC is just linking to USDA sites and not putting that information together.
That’s a disadvantage because we need a more integrated response. I think we need a one-stop shop for H5 in terms of all the species that it can be impacting.
What other recommendations do you have for how to control this?
We have time right now to reassess what’s happened and figure out what we can do. We can predict which states will be entryways for the migratory birds and think about how we can protect the at-risk dairy cows, cattle, and poultry from migratory birds that may be carrying this virus back north in the fall. We just can’t take our eye off the target.
