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In recent news appearances, Department of Health and Human Services Secretary Robert F. Kennedy Jr. has suggested allowing bird flu to spread in poultry flocks unchecked. Scientists say that’s risky because it gives the virus more opportunities to replicate, increasing the chance it could change to spread easily among humans.
Avian influenza, or bird flu, has been spreading in U.S. dairy cows for more than a year now and has infected several dozen dairy workers. The virus also has infected flocks of chickens and other poultry in the U.S. since 2022, leading to the deaths of more than 168 million birds, infections in poultry workers and high egg prices.
“We’ve in fact said to [the U.S. Department of Agriculture] that they should consider maybe the possibility of letting it run through the flock so that we can identify the birds and preserve the birds that are immune to it,” Kennedy said of bird flu in an interview with medical correspondent Dr. Marc Siegel. The conversation aired March 4 on Fox Nation.
“Most of our scientists are against the culling operation,” Kennedy said in an interview with Sean Hannity, which aired on Fox News March 11. Kennedy advocated testing therapeutics in flocks and again suggested looking for birds with “a genetic inclination for immunity.”
Researchers have acknowledged that culling on its own has not stopped bird flu from infecting poultry. But they said Kennedy’s strategy is risky and unlikely to yield a breakthrough in the search for bird flu therapeutics or genetic resistance.
“If someone is going to say well, we should let the virus just go unchecked and follow RFK Jr.’s suggestion, we’re going to exacerbate the problem,” Dr. Maurice Pitesky, an associate professor at University of California, Davis, Veterinary Medicine Cooperative Extension, told us. “There’s no scenario where that is a good idea.”
“Why do we want to give the virus a leg up? Why do we want to give it an advantage and let it do its worst without being checked?” Ian Brown, group leader of avian virology at the Pirbright Institute in the U.K., asked us. “That doesn’t feel terribly logical.”
Letting bird flu run through poultry flocks is “not advisable and this will cause serious harm to poultry and put other animals at risk, but also humans who will have to manage the culling/clean-up, which poses a huge biosecurity risk,” Saskia Popescu, an infectious disease epidemiologist at the University of Maryland School of Medicine, told us in an email.
Meanwhile, Kennedy left out important context about the risk of bird flu. And he misleadingly claimed that vaccinating poultry would turn birds into “mutation factories,” when researchers say that vaccinating birds could be one possible way of mitigating agricultural harm and reducing risks to people.
Kennedy is in charge of HHS, not the USDA, so it is unclear how much his views will influence the policy on culling or vaccinating birds. On the human health side, lawmakers and scientists recently have raised concerns that HHS is threatening pandemic preparedness by pulling back funding to states being used to control infectious disease, embarking on a massive reduction in HHS staff and reportedly reevaluating a contract for research into bird flu mRNA vaccines.
Secretary of Agriculture Brooke Rollins in a Feb. 26 Fox News interview indicated USDA might try out a pilot program to build a “safe perimeter” around some flocks to “see if there is a way forward where the immunity and the genetics and the DNA become part of this.”
However, the USDA affirmed to us via email that its policy is still to require culling. “The United States will continue to follow our established stamping out policy,” in keeping with international guidelines, an agency spokesperson said, and also will work to “develop innovative strategies (including alternative response activities) and ensure we use every tool at our disposal” to fight bird flu.
In late February, the USDA announced a $1 billion strategy to combat bird flu, which includes funds dedicated to developing vaccines for poultry and for improving biosecurity on farms. Good biosecurity can help prevent bird flu from being introduced to farms in the first place.
Letting Bird Flu Spread in Poultry Is Risky
H5N1 bird flu — the type causing the current outbreak in the U.S. — spreads rapidly in chickens and is highly lethal. USDA policy is to kill all the birds in a flock once H5N1 is detected. This culling process, also referred to as depopulation, reduces bird flu’s ability replicate, mutate and spread.
In his interview with Hannity, Kennedy blamed high egg prices on culling. “We’ve killed 166 million chickens,” Kennedy said. “That’s why we have an egg crisis.”
But bird flu is the root cause of the bird deaths. These birds “would die anyway if they were not depopulated,” Brown said, explaining that the “lethality is pretty close to 100%.” The hens would stop laying eggs early in their infection, he added.
When infection is allowed to take its course, poultry “die quite a horrible death,” Brown said, so there is also an animal welfare issue with not culling.
The most likely outcome of stopping culling, Pitesky said, would be more bird deaths as the virus spread unchecked, ultimately reducing the country’s food security.
“The quicker you depopulate, the quicker you can prevent disease transmission from that facility to other facilities or to wild birds that are in that area that are then going to transmit the disease to other facilities,” Pitesky said.
Stopping culling could increase the risk of bird flu changing in dangerous ways. “The more opportunities the virus has to replicate, the more opportunities it has to mutate and reassort with all kinds of different strains,” Pitesky said.
Kennedy was also wrong to almost entirely blame bird flu cases in humans on culling. “Almost all of the people who have gotten sick were workers who were involved in the culling operations,” he told Siegel.
“That’s inaccurate,” Popescu said. According to the Centers for Disease Control and Prevention, 24 out of 70 U.S. human bird flu cases cave been in people exposed via poultry farms and culling operations.
There have been cases “related to culling, but this is also in relation to poultry exposure overall – culling is a necessary practice to avoid additional exposure (humans and animals), and frankly it’s a horrific illness for birds,” Popescu said.
Strategy Unlikely to Identify Flu-Resistant Chickens
Researchers said that stopping culling in order to find resistant birds or new therapeutics was unlikely to be effective. “People have been trying to breed genetic lines that are resistant to flu for some years now and have generally failed to succeed,” Brown said.
There has been research into whether some birds might have genes that could provide flu resistance, Pitesky said, but this work is done in poultry being raised in villages in Africa and Asia that have more genetic variation.
Commercial chickens in the U.S. are bred to be as genetically identical as possible so that they will grow at the same rate, Pitesky added. These poultry are the “least ideal population” to test whether it’s possible to identify birds with genetic resistance to H5N1, he said.
Pitesky also said that before testing a therapeutic in the field, “you ultimately need some indication that it’s going to work.”
“The biggest issue is we don’t have anything in the pipeline right now, as far as I know, that there’s any indication it could be curative of a viral infection like this in poultry,” he said.
Brown said that there have been concerns about whether therapeutics for chickens could be cost-effective, “even if they could do the job, which I doubt.”
“I do think we do need to think outside the box, but that is not a viable outside-the-box scenario,” Pitesky said, referring to Kennedy’s proposal for finding resistant chickens.
Vaccinating Poultry Could Curb Bird Flu
One possible way to protect chickens would be to vaccinate them, Brown said.
But in his conversation with Hannity, Kennedy misleadingly dismissed vaccination as a strategy that could harm human health. “All of my agencies have advised against vaccination of birds because if you vaccinate with a leaky vaccine — in other words, a vaccine that does not provide sterilizing immunity, that does not absolutely protect against the disease — you turn those flocks into mutation factories,” Kennedy said.
Brown said that vaccination would reduce illness in birds and their ability to spread the virus. Bird flu vaccines do not completely prevent infection, and vaccination could favor versions of the virus that aren’t as well targeted by the vaccine. However, there isn’t evidence that vaccination would “generate some monster virus that can infect people,” he said.
Poultry vaccines are available, and countries including Mexico, France, Egypt and China use vaccines against bird flu in poultry.
The “claim that poultry vaccination will ‘turn those birds into mutant factories’ is incorrect,” virologist Angela Rasmussen of the University of Saskatchewan said in a social media thread. Vaccination in China against another type of bird flu virus, H7N9, did favor survival of flu genotypes that could evade the vaccine, she said. But researchers found that the “variants that emerged were less adapted to infect humans,” Rasmussen said, and vaccinating the birds “basically stopped human infections.”
“So yes, RNA viruses like flu can mutate & vaccination creates selection pressures driving their evolution,” Rasmussen said. “But that doesn’t turn chickens into mutant factories & reduces the risk to humans.”
There are policy and logistical barriers to vaccinating chickens in the U.S. Brown explained, for instance, that some countries do not allow imports from countries that vaccinate their poultry. The laying industry in the U.S. does not have a substantial export business and is for vaccinating poultry. The meat industry, also called the broiler industry, exports large quantities of chicken and is against vaccination due to the trade embargoes.
As we’ve written, USDA is funding vaccine research. In response to a March 26 question from Forbes about Kennedy’s poultry vaccine comments, asked during an impromptu interview outside the White House, Rollins did not comment specifically but emphasized that multiple agencies would work together to curb bird flu.
Risks of Bird Flu
The CDC and the World Health Organization currently consider the risk of H5N1 bird flu to the general public to be low. However, public health experts still recommend that people take precautions, such as avoiding raw milk and using caution around wild birds and other potentially infected animals.
Scientists also have emphasized that the risk level of bird flu could change very quickly if the virus changes to more readily infect and spread among humans.
Kennedy — who has advocated deregulating raw milk in the past — left out this context in talking about the food supply. “It’s not transmitted through eggs or through dairy products,” he told Siegel.
“As far as we know, you cannot get it from an egg or milk or meat from an infected animal,” he said to Hannity.
There have been no documented human cases of bird flu in the U.S. resulting from eating eggs, milk or meat. Birds with flu stop laying eggs early in the course of their infection, and the virus isn’t found in high amounts in eggs, Pitesky said. For eggs, “I’d be more concerned about salmonella than I would about avian influenza,” he added.
“Dairy is different,” Pitesky said, saying that raw milk is “dangerous,” both due to the potential presence of bird flu and due to other microbes. In cows, bird flu is found at the highest levels in the udder and milk. Pasteurization kills the bird flu virus, but it has been shown to persist in raw milk and raw milk products.
Cats have died from H5N1 bird flu after drinking raw milk. “If someone is going to tell me, let’s wait until a human dies … I’m not willing to take that chance,” Pitesky said.
Raw meat pet foods have also killed cats.
Kennedy also said that B3.13, the version of bird flu that spread to cows in late 2023, is “not very dangerous to humans,” adding that it “is not something that we’re deeply concerned about.” He said to Siegel that the D1.1 version of the virus, which has been found in wild birds and poultry and also recently spread to cow herds, is “more dangerous.”
To date, the B3.13 genotype has caused mild disease in humans. D1.1 and a related version of the virus, called D1.3, have led to three severe bird flu cases in humans in the U.S., including one death. The severe cases occurred in two people with backyard poultry and one worker who was culling diseased poultry.
However, scientists cautioned against complacency in the response to any version of the virus. “It only needs to acquire a couple of mutations” to become more dangerous to humans, Brown said. “That risk profile might change.”
“Epidemiologists like me are wary of drawing premature conclusions about severity,” Caitlin Rivers of Johns Hopkins Bloomberg School of Public Health wrote in a recent New York Times opinion piece. She cautioned against drawing firm conclusions from small numbers of cases occurring largely in dairy workers, when people with high-risk health conditions or the very old or young might be underrepresented.
“I fear that the apparent mildness of infections in the United States has confounded calls to act more decisively,” Rivers wrote.
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