On H5N1, ‘Our Focus Should Be on Protecting the Workers’.

On H5N1, ‘Our Focus Should Be on Protecting the Workers’
Following the first US human and domestic cat deaths from H5N1, David Hamer and Jessica Leibler weigh in on what we should be doing to minimize the rapidly growing threat of avian flu in the year ahead.
The first US death from avian influenza earlier this month marked a new turn in the rapidly evolving H5N1 virus, which had previously caused mostly mild symptoms among the 67 people who contracted it across the country over the last year.
The Louisiana patient who died represented one of two reported severe cases of the virus in North America, the second occurring in a Canadian teen who almost died.
And the virus shows no signs of curbing its spread. H5N1 has now infected more than 130 million commercial and backyard poultry, thousands of wild birds, and at least 928 dairy herds. It has also made an unprecedented jump to pigs and killed domesticated cats who were exposed to the virus through raw milk or food.
While federal officials maintain there is currently no evidence of human-to-human transmission, the gaps in knowledge on how and to what extent the H5N1 bird flu is spreading amongst various species are undeniable. The majority of reported cases have afflicted farm workers with direct contact with poultry or cattle, but at least three cases—two in California and one in Missouri—involve individuals who have had no known contact with wild birds or farm animals, and the cause of their infection remains unknown.
“Even though we have been aware of H5N1 since the mid-90s and have observed hundreds of documented cases worldwide over the years, we still don’t have a tremendous amount of information as to what human infection with H5N1 looks like,” says Jessica Leibler, associate professor of environmental health. “Most people who have been identified with the virus over the last 30 years have been detected because they were severely ill. The mortality rate overall for humans is very high—about 50 percent—but it’s unclear what the true denominator is to that equation, including how many people who may have been infected and were asymptomatic or mildly ill.”
What we can surmise is that the recent severe and deadly infections, new and continued spread among birds, cattle, and other mammals, and undetermined origin of multiple human cases suggest that avian flu is likely mutating in both humans and animals. The concern among experts is that a few more mutations could lead to human-to-human transmission.
“What I worry about is that this virus could have a recombination event with a more mundane influenza virus and change enough to spread person to person. And then we could potentially have a big epidemic on our hands,” says Davidson Hamer, professor of global health.
After harsh criticism for a delay in conducting widespread testing and monitoring of H5N1 on dairy farms and among the most affected groups—farm workers and others who have direct contact with cattle or poultry, the US Department of Agriculture (USDA) announced a federal order for mandatory national milk testing, in partnership with veterinarians and state and local health officials, to monitor and limit the spread of the virus among dairy herds. The testing began in six states in December and has now expanded to 28 states.
It is also unclear how the incoming Trump administration will handle the bird flu threat, with the future of the Office of Pandemic Preparedness and Response in question, and the documented history of inaccurate statements by Health and Human Services Secretary nominee Robert F. Kennedy, Jr. on bird flu, vaccines, and disease spread. In the last week before Trump resumes office, Hamer and Leibler discuss Hamer and Leibler discuss what we know about H5N1 transmission pathways, what we can do to protect farm workers, and the actions they hope the next administration will take to combat this threat and prevent it from becoming the world’s next pandemic.the next administration will do to combat this threat and prevent it from becoming the world’s next pandemic.
Q&A
with Jessica Leibler and Davidson Hamer
Does the first US human death from H5N1—and possible mutation of the virus—change your level of concern about the current outbreaks?
HAMER: This is a highly concerning and sad event. My level of concern remains high, but as of yet, there is still no solid evidence of person-to-person transmission of H5N1 in the U.S. or elsewhere. We need to sustain and enhance surveillance activities among wild and domestic animal populations as well as, of course, humans. We also need to be prepared with adequate stockpiles of vaccines and treatments (neuraminidase inhibitors) for the time when a genetic reassortment happens and this strain of influenza becomes more readily spread among people.
LEIBLER: One of the things about H5N1 that I think is under-appreciated by the general public is how incredibly prevalent the virus is in wild birds and in many other animal species right now, such as marine mammals and other wild animals. We’re continuing to see this explosive encroachment of the virus into wild birds, wild mammals, and even domesticated animal populations, that hasn’t been seen before. The virus has successfully expanded its species range very dramatically in a short period of time.
The areas of real concern are where the virus can cross over into human populations, and those nexus spots are our food system,including industrial production of animals for food and domesticated animal production. Small-scale animal holders, including people who own backyard chickens and other smaller operations distinct from huge corporations, are also at risk, as are people with pets that might be outside and come into our homes.
The virus has also jumped to pigs in the last several months. What is unique—and concerning—about the crossover into this species?
LEIBLER: Pigs are able to be infected by viruses that are adapted for different kinds of animals. Influenza virus can have very niche species that they circulate in, and pigs are interesting in that they can become infected with avian viruses, and they can also become infected with human influenza Aso they serve as a mixing bowl of different types of viruses. There can be recombination or reassortment processes that allow for the emergence of viruses that retain animal components and acquire capabilities for human-to-human transmission. For a long time it was believed that pigs were the only mixing vessel like this, but it’s now known that other animals can serve in this function, as well.
Last month, the USDA announced the start of a national milk testing strategy, beginning with six states. Is this the right next step in understanding how this virus is spreading?
LEIBLER: It’s well known that raw, unpasteurized milk carries a lot of pathogens and poses a real risk from an infectious disease standpoint. This is one of the areas that is highly politicized now, given the political conversation about our potential public health leaders in the next administration, but I find it unsurprising that raw milk might broadly have pathogenic agents, including H5N1, especially in states where the virus has already been detected in dairy populations and is known to be circulating.
It’s important to note that raw milk is not the finished milk product for the industrialized dairies that we are talking about. Raw milk is the upstream product that is then pasteurized to produce the final consumer product. So testing raw milk is not identifying pathogens in the consumer milk product, and pasteurization has been demonstrated to deactivate H5N1 Drinking raw milk is risky in general, but that was known before this outbreak of H5N1.
Understanding the extent of human exposure seems like it should be the most important thing right now, perhaps more important than assessing the unfinished milk supply, and that kind of human-based surveillance has really not been done in any broad way. As this virus circulates among dairy farms, it matters less as an urgent public health crisis to know if it’s being transmitted through milk, feces, or the cow’s respiratory secretions; our focus should be on protecting the workers. This is not to say that studying raw milk is not important, but I wouldn’t opt to focus limited resources on milk testing in lieu of determining how to protect humans at that animal-to-human interface.
HAMER: I agree. Part of the challenge is that a lot of these workers are migrant laborers, so they may be undocumented, and they’re often working in hot, humid conditions, where wearing protective gear can be uncomfortable. With that said, we need to offer them this protection to minimize their personal risk of becoming infected.
There are still so many research questions to explore—one is qualitative research with farm workers to try and understand their issues and their willingness to receive the influenza vaccine, as well as the barriers and facilitators of wearing PPE. Perhaps a pair of gloves and goggles would be sufficient. A lot of the initial H5N1 cases involved people getting infected through their eyes, because they had contact with the udder and then presumably rubbed their faces. So, perhaps minimizing contact would be effective.
How can public health advocates help ensure that farm workers receive these protections?
LEIBLER: There have been gaps in the past in using our collective public health understanding in reaching this workforce. We know that this is predominantly a disadvantaged workforce. We should use all of the things that we know about community engagement and health communication and outreach strategies to engage with these workers in solving problems. Public health as an entity has talked a lot about these workers, but hasn’t really involved them in thinking about solutions and interventions. And so there’s a lot of conversation about what should be done with workers, or what should be done to workers, and not so much conversation actually with workers and their representatives and their organizations. As these plans are developed to protect workers, I hope these conversations actually involve workers to be able to develop plans that are realistic.
For example, the full set of PPE tools that might be perfectly advised from a viral protection standpoint may be totally impractical for use in an animal facility because of heat or dust, for example. But if those lines of communication are not open, it can be hard to see that. There also are opportunities here to engage with a hard-to-reach workforce with multiple components of public health outreach, especially around vaccination. These workers may receive very limited healthcare; maybe this is an access point to engage these communities more broadly in healthcare. We need to think about all of the strategies that we have in our public health toolkit to connect with difficult-to-reach populations and to apply that, and not just talk about this workforce in the abstract.
What else are we learning about H5N1 symptoms and spread?
HAMER: Some of the initial cases involved farmers who mainly had ocular symptoms, such as conjunctivitis. This may have resulted from milking cows, so they probably inoculated themselves by rubbing their eyes. Once the virus gets into your system, it may cause a deeper infection. Others have had respiratory symptoms. But we still don’t fully understand how it’s jumping from cattle to humans. Some of it is likely through contact with the milk, but it could also be spread when the cow sniffles or sneezes, and sheds virus-laden aerosol. This aspect of transmission is an open research question.
LEIBLER: Being exposed to fecal waste of the animals is another viable exposure pathway for most influenza viruses. The animals put their face into a trough to drink and to eat, so workers who are working with feed and water for the animals might be exposed through a respiratory pathway. We should also think about aerosolized pathogens, given dust in these facilities. .
Another question is exposure through contact with raw meat, and whether slaughterhouse workers are exposed to infectious virus. Thinking about this holistically alongside what we know about other animal-to-human pathogen transmission events in the context of industrial food animal production will be really helpful in identifying the most productive strategies that we can implement right now to protect the workforce, rather than waiting to have a full diagnostic understanding of every element of viral transmission.
The goal should be to protect people across potential transmission points, even before the epidemiology of transmission is fully understood.
Have there been advances in the last several months on vaccine development?
HAMER: There has been further research on the development of H5N1-specific vaccines. The Office of Pandemic Preparedness and Response (OPPR)—which will likely be eliminated under the next administration—has stockpiled a lot of doses of an H5N1 vaccine, but I don’t know the data on how well it works. They’ve developed it the same way they’ve developed other influenza vaccines, so it should be immunogenic and safe. Three vaccines are licensed. Two are adjuvant, which means they stimulate an immune response. They may cause a few more side effects, but they produce a stronger immune response. There is a plan to produce 4.8 million doses of vaccine that targets the clade strain circulating globally and infecting US dairy herds, and some farm workers. Health officials should be thinking about immunizing frontline workers, such as dairy farmers or anybody having direct contact with cattle and so forth.
What actions do you hope the Trump administration will take to minimize risk from this virus, or any infectious diseases?
LEIBLER: Supporting vaccine uptake is an important priority. While vaccination may support H5N1 prevention efforts, these discussions are happening alongside a solid amount of vaccine hesitancy and misinformation that, in part, is being delivered on behalf of the new administration, but was also deeply entrenched during COVID. It’s an open question how a potential H5N1 vaccine might be received by the public in this environment, and I think there is the concern that the continued drumbeat around vaccine hesitancy is going to weaken our ability to use this tool in our toolkit to help address this concern.
The other major thing on my mind around zoonotic outbreaks is that to manage them requires really careful attention to the intersections between government agencies. A pandemic emergence from animals crosses multiple government agencies. It involves the CDC, OSHA, the USDA, the FDA. And oftentimes the intersections between these agencies are not as strong as we might want them to be. My core guidance from a policy standpoint is to make sure that there are regular channels for communication among the agencies, and not to weaken those links, because they’re particularly important when you have a disease outbreak that originates in animals. These agencies need to talk to each other rapidly and effectively.
HAMER: At the moment, I am actually most worried about potential measles outbreaks. I would like the Trump administration to not do anything that would limit the use of the MMR vaccine, such as eliminating them from school requirements. Trump’s administration has also talked about trying to investigate the association with autism, which has been completely debunked. There are many large, population-level studies that show no association, so they shouldn’t be bringing this issue up again. And if they abolish school requirements, there will be more people saying ‘I’m not going to vaccinate my kids.’ Then you’re going to have a greater proportion of the population that’s unvaccinated. Measles is also highly transmissible. The reproductive level is 10 to 15, or 12 to 18. Initially with COVID, we thought it was around 2 or 2.5, and then it came down to 1 or 2. That means that one to two people might become infected with COVID for each person that is infected. Twelve to 18 people who are not immune to measles through vaccination or prior infection could get it for every person that is infected. I’m worried about measles, but we could have more problems with pertussis, and even polio.
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