What you need to know about bird flu

A Louisiana resident has died from bird flu. Just as during the COVID outbreak, there's a lot of misinformation circulating about H5N1.

We'll get a clear assessment on bird flu, how it's changing, and efforts to control it.

Meghan Davis, molecular epidemiologist. Associate professor, Johns Hopkins University Bloomberg School of Public Health.

Dr. Nirav Shah, principal deputy director of the Center for the Disease Control and Prevention.

Dr. Seema Lakdawala, co-director, Center for Transmission of Airborne Pathogens at Emory University School of Medicine. Associate professor in the department of microbiology and immunology.

Part I

MEGHNA CHAKRABARTI: If listening to an episode about another disease outbreak is the last thing you want to do, I completely understand. There are more pressing things in life right now, and I'm particularly thinking of everyone who is coping with very harsh weather across this country, and the impacts of that weather, and the devastating wildfires, particularly in Southern California, thinking of you all.

However, just as there was with COVID, right now there's a lot of information and misinformation floating around about H5N1, the current bird flu. So today we're going to go back to basics, and do the kind of show we frequently did in the first year of COVID. We're going to ask what do we know about this disease, what do we currently not know, and what do we need to understand to ... better protect everyone.

So to do that, I'm joined by Meghan Davis. She's a molecular epidemiologist and associate professor at the Johns Hopkins University Bloomberg School of Public Health. Professor Davis, welcome to On Point.

MEGHAN DAVIS: Thanks for having me.

CHAKRABARTI: So I wanted to start with what's been in the headlines recently about H5N1 in the United States, and that is the first U.S. fatality. The first person to die as a result of this disease. It happened in Louisiana. Is this cause for concern?

DAVIS: Certainly, we're always concerned about avian influenza. It's a virus that we know is adaptable, and it has caused major pandemics in the past. What we're dealing with here is a zoonotic avian influenza.

And unfortunately, the sad news about the Louisiana case is also that they may have had exposure to wild birds or backyard poultry. So they may have had exposure that way to animals. This is pretty typical of the severe cases of avian influenza that we can see globally. And that is that they tend to be sporadic.

They just pop up, you'll get a single case, maybe a couple, and then you won't see it for a little while, so certainly tragic and something to be concerned about, but not necessarily on the next step towards a pandemic where we would be concerned about human-to-human transmission.

CHAKRABARTI: Okay, that's good to know.

And more specifically, this particular person in Louisiana, as far as I understand, the Louisiana Department of Health has said that the person was over 65, had underlying health issues as well. So would that have made them more susceptible, more vulnerable to the effects of H5N1?

DAVIS: When you have comorbidities, meaning when you have other health problems, it can make your clinical course of disease more complicated. Meaning that things can come up that might not come up in an otherwise healthy person. That said, we also know that there was a teenager in Canada who also got severely ill from a strain of avian influenza, and had to be hospitalized.

And so this is a person who might be, in theory, a little bit healthier than someone who is over the age of 65. The reason why I ask is because, as you can guess, COVID and our collective experience of it really hangs over this entire conversation. And one of the things I am sensitive to is that many people, perhaps rightly said, after a couple of years of COVID, they were thinking, why do I have to be worried about this anymore?

Because I am younger, I am healthier. I don't have comorbidities. And so it became hard for them to take seriously and understandably, some of the measures that public health officials were suggesting they take. We don't want to repeat that mistake here with bird flu, right?

DAVIS: What we're seeing is actually that most of our cases are in some of our healthiest adults, meaning people who can work, and not just work, but work on a farm.

If anyone's ever worked on a farm, you know it's a full contact sport. This is very difficult work. It's often long hours with a lot of physical exertion. So it takes a particularly healthy kind of person to be able to do this, but this is what most of our cases of avian influenza in the United States are, and we're now at over 60 cases.

Again, most of them are poultry or dairy workers.

CHAKRABARTI: And when we say severe? What's your definition of severe?

DAVIS: Severe in terms of avian influenza often means being hospitalized and having symptoms that could be life threatening. Luckily, what we're seeing in most of the workers is more mild disease. Now, when I say mild, mild on the scale of not hospitalized.

They do get conjunctivitis and upper respiratory symptoms. And looking at some of the photos of the conjunctivitis, I would say that's not a mild conjunctivitis. It's just a mild case of avian influenza.

CHAKRABARTI: So conjunctivitis, meaning it's in their eyes.

DAVIS: Like pink eye. Yeah.

CHAKRABARTI: Okay. And so then, but to stay focused on the fact, on the important fact is you're raising that most of these cases are amongst agriculture and farmworkers specifically right now.

I just want to underscore that means that we are not currently seeing human to human transmission.

DAVIS: That is correct. We have not yet documented any human-to-human transmission. If we would start to see that, because we know that these strains can change over time, that would be cause for greater concern.

So that's why I say it's a reassuring and concerning story, all at the same time. The concerning piece is that this is a virus that can shift, and it can change, it can become more virulent, and it can become more adapted to human-to-human transmission. And that would really put it on a path towards being able to cause greater disease in humans that we're seeing.

CHAKRABARTI: Okay.

DAVIS: But to be fair, we already see a lot of disease in animals, and we are seeing animal to animal transmission.

CHAKRABARTI: A lot of H5N1 in animals, yes.

DAVIS: H5N1, correct.

CHAKRABARTI: Yeah, okay. But let's go back a little bit given what you just said. Can you walk us through what led to first identifying this particular round of H5N1 as a cause for concern amongst public health officials?

DAVIS: Avian influenza is always a cause for concern among public health officials. It is reportable disease. Anytime we see it, we notify the global authorities, and we take measures to really intervene, to try to prevent further spread. And highly pathogenic avian influenza, otherwise known as HPAI or high path is something that pops up from time to time.

Our story for H5N1. This particular clade, which is 2.3.4.4b, really begins globally in like 2020, 2021. And it was first detected in North America in late 2021 in Canada. And very quickly thereafter, in early 2022, in the United States, affecting wild birds and commercial poultry. We had our first human case in 2022.

After that, we had a plot twist, and this occurred in February or March of 2024, which is when we first identified it in dairy cows. I say plot twist because when we think influenza viruses, we think about poultry, so chickens and turkeys, and we think about swine, so pigs. We don't typically think about cows, and it does something very strange in the cows.

It is remarkably trophic, meaning it has a laser focus on the udder. So these are the mammary glands. This is what produces the milk. And so you get actually your highest virus coming into the milk that the cow is producing.

CHAKRABARTI: Just for, so we are all on the same page regarding terminology. You said clade.

Is that the word for variant or version when it comes to bird flu?

DAVIS: We have a couple different ones, right? So you have the avian, you have the influenza viruses. Among these, you have your swine and avian influenza viruses. Then you have these different, subtypes.

Your H5N1s, H7s, H1s, etc. And beneath those you have clades, and then within those, you have genotypes. People will sometimes say strain, you'll hear a lot of different terms flying around. But think of these as like a genealogy. What we have within H5 is this particular clade causing a problem, and within that we've got some siblings.

CHAKRABARTI: Okay, so if I said strain, though, I wouldn't be misspeaking.

DAVIS: I think you're fine.

CHAKRABARTI: Okay, good. Because I both want to be fully accurate scientifically, but also keep this accessible, right? For folks. But clade, I have to be honest, I hadn't heard of that one until learning more about avian flu. So about the cattle, the spread to dairy cows, do we know how that happened? Because you said there's the plot twist.

DAVIS: Yeah. Yeah. We think it was a single event where it probably came from a wild bird into a cow, probably in Texas. There are a lot of probabilities here. And the reason is that we didn't directly witness it.

There was no one like standing watch saying, Oh, Hey, there's a bird and a cow. And now the cow's got mastitis. So what we're inferring is actually some pretty interesting detective work, looking at the genetic sequence of this particular genotype or strain and tracing it back to see when did it probably happen?

And then watching it as it moves forward, as it continues to transmit from cow to cow and from cows into other animals, like back into poultry, back into wild birds, into cats, and into people, particularly these workers. And what we've seen is that this is a relatively stable genotype, meaning it's not shifting a whole lot, but there are a few changes that we are watching and monitoring.

CHAKRABARTI: When I guess, when I'm saying how did it make that jump? Perhaps my question is actually more rudimentary even than like the specific genotype. Because if it came from a wild bird, are we talking potentially bird droppings? I don't, did the bird sneeze on the cow? I don't mean to be flip, but honestly, because when it comes to interspecies jumping of zoonotic diseases, in the past, we've known if there's close contact or when humans mass farm animals, that makes sense, right?

Because it allows a certain reservoir of disease to build up. But between wild bird and cows, do you have any theories on that?

DAVIS: Oh, I have several. Let me paint you, let me paint you a picture of a dairy farm, especially one that might be in Texas, because the way they look will be different. If you're in Lancaster, Pennsylvania, where I used to be a dairy practitioner, you've got these adorable kind of closed barns, right?

With the beautiful emblems on them, and the cows will go out sometimes. What we see in more dry lot dairies, so this is when it's really hot, we often will see something called kind of freestyle barns. So they have no sides, they have a roof and the sides are completely open. And now you have these cows and what do you feed cows?

Will you feed them things that include grains, which can be very attractive to birds? So what I would see when I would go on these larger dry lot farms is the birds are just hanging out with the cows. They might be roosting above them in the rafters. They might actually be riding on the back of the cow.

You'll sometimes see that. They could be rooting around in the feed. And so it's very easy for you to think about how droppings might get to a place where cows can either ingest them or maybe even come into direct contact with them. For example, if a bird defecates and then the cow lays down on that area, then you could even potentially have direct contact with the udder. We don't know.

Part II

CHAKRABARTI: Professor Davis, I want to just take a little bit of a tangent here. Because I'll have you know that the senior editor of our show is from Pennsylvania, and I'm convinced she's running a conspiracy to make Pennsylvania pop up in very unexpected ways on this program. So tell me a little bit more about your time as a dairy practitioner in Lancaster, Pennsylvania.

DAVIS: Technically Lebanon, actually.

CHAKRABARTI: Okay, Lebanon.

DAVIS: Which is just north of Lancaster.

CHAKRABARTI: Sorry, Pennsylvania.

DAVIS: ... Pennsylvania is a really great dairy state, and there are a lot of different kinds of dairy farms there. So I worked primarily with Amish and Mennonite dairy farmers, which was a really interesting way to practice.

Had a great time. I trained in California though. I had experience across the wide range of different styles of dairy farming that we have in this country.

CHAKRABARTI: Oh, interesting. And what did you practice as a dairy practitioner?

DAVIS: Oh, so as a dairy practitioner, you do lots of different kinds of things.

You are a consultant for your farmer in terms of the production of the cows. You look at the engineering of the barns and give them advice on that. You look at how the cows are doing reproductively, because you have to have a calf to come into lactation, meaning to give milk. So giving birth is a really important part of a dairy farm.

So you pay a lot of attention to that, and then you also take care of the sick cows.

CHAKRABARTI: So actually, this is really good to know, right? Because the focus, understandably, right now, is on the agriculture industry, which is where the vast majority of the cases of H5N1 are popping up. At this point in time, Professor Davis, how would you describe, is there a major threat to the ag industry in this country because of bird flu right now?

DAVIS: Yes, we've had millions of birds lost, and this is broiler chickens that we use for meat, layer chickens that we use for eggs, turkeys and other species, and now we have these impacts to dairy cows. And the impacts, we still don't know exactly what the long-term influence is going to be. We recognize that some cows can get quite sick and have real losses in production, meaning they were giving milk and giving lots of milk, and now the udder has really suffered a big setback and is having trouble getting started again.

What that means for the cow over many years, we will need many years to identify. I think the biggest challenge though is currently in California, which is the leading dairy state in the country. And where we are seeing most of our current cases in dairy herds as well as in nearby poultry or getting the same genotype or strain that the dairy cows have.

And in these farms, you could have a real impact for the consumer, because you now have so many farms that have been affected, that your supply of milk is now dramatically shifted.

CHAKRABARTI: We've already seen that with eggs. Because of all the — Go ahead.

DAVIS: Yes, and egg prices, yes.

CHAKRABARTI: Yeah, let me go back to something you said.

You said we've lost so many birds, meaning they are being culled, right? And what is the threshold that is set for when the decision is made to cull birds on a poultry farm? Is it one case of H5N1 or what?

DAVIS: Yes, any detection. The thing to know, though, is that with highly pathogenic avian influenza, the highly pathogenic refers to what it does to the birds.

So you can close your barn at night, go back home, come back the next morning, and you can have half the flock affected, and some of them already dead. It can happen really quickly. So when we say that we cull the birds, we're typically culling animals who are not necessarily likely to survive anyway.

So it is a public health measure, but it's also something that, in terms of the disease in the birds, is already quite severe. And it's not the same in dairy cows, so we're not doing that kind of control measure in dairy cows.

CHAKRABARTI: But we are talking about a farm potentially having to cull all of its poultry, right?

DAVIS: Correct.

CHAKRABARTI: Is that what's been happening?

DAVIS: Yes. And so you have some farms that have millions of animals.

CHAKRABARTI: Is this working though? H5N1 is still circulating.

DAVIS: So the United States Department of Agriculture recently shifted its indemnification program. So what happens is the federal government steps in to help out the farmers when they have to do this.

Because some of this is a public health decision as opposed to an individual decision by a producer, right? So what they do is they give some money towards each of the birds that are lost. They changed their program recently to require that someone come out and check the biosecurity of the farm prior to moving forward with restocking, so getting new birds in.

And the reason for this is to try to prevent it from happening over and over again. So the poultry industry has often, on some farms, pretty tight biosecurity. Meaning that there are at least disinfectant baths for your boots before you go in, and some places even will have you, if you work there or come on to the facility, change your clothes or even shower in and shower out.

That way, nothing from the outside can be brought in, and they can use enclosures for the barns to make sure that you don't have wild birds coming into the facility.

CHAKRABARTI: So do you think that will help though? Because I keep coming back to the fact that, as you said, millions of birds are being culled right now, but it doesn't seem as if we're seeing any abatement in the spread.

DAVIS: Yeah. In part, because we have such severe cases. Such transmission in California, in part, because of the Pacific flyway. It's like the migratory birds superhighway. And so what we tend to see is when you have a lot of bird migration, you'll find that the virus will follow that. So there will be periods of time when it pops up and then goes away.

What we'd seen in the past, before H5N1, was that this might happen periodically. So we'd have a season of it, and then it would actually go away. But what we're finding with H5N1 is that it's following the flyway kind of north to south and south to north and vice versa, right? Just back and forth. And it's been continuing over many years, which is really unusual.

So this particular H5N1 has greater staying power than some of the prior avian influences that we have been dealing with recently.

CHAKRABARTI: Oh, that's interesting. So I'm going to put a little pin in that and come back to it. Because I wonder if there's a line of questioning here about agricultural practices, as a whole, over the long run.

But I also want to just, we're going to talk about humans in a second, but that twist of an avian influenza jumping to a cow, I just want to underscore one of the reasons why this is a twist. Because birds are a completely different part of the evolutionary tree than mammals, right?

Have we seen this kind of like big jump in a zoonotic influenza before?

DAVIS: H5N1 has been actually discovered in quite a few different mammal species. You may have remembered that there was a marine mammal die off, particularly in South America, just a couple years ago, and that was caused by H5N1. So we know that it can get into multiple different kinds of mammals, and that's a big concern from a public health perspective.

We're also a little bit worried, and we don't know a lot yet about it, that it's possible for mice to get infected. This is an issue, because the mice may be one route that we see transmission between farms. We also know that shared equipment, shared personnel, and movement of animals is another one. But we also are concerned about the potential for it to establish within hosts that aren't birds.

And what would happen to the virus then if it's in a mammalian host and has more opportunities to, with a little switch or shift in the genome, to become more adapted to mammals. And that means that it could potentially spread more easily from person to person.

CHAKRABARTI: Okay. So with that in mind, I do want to underscore the fact that this is a major issue to farmers in the agriculture industry.

Everything that you've described makes it top of mind for people who are in the world of agriculture in this country. But for everybody else, I don't blame folks for thinking she's saying repeatedly that it's not yet spreading from human to human. So if in the times that we do see it pop up in people, it should be easy to contain and has thus, has been thus far.

So why should I worry?

DAVIS: So certainly, one of my big concerns as a veterinarian is that house cats are getting it. And we know that ferrets, dogs and cats are susceptible hosts, meaning they can get it. And initially, the cases in cats that we saw were cats that were on these dairy farms. Now, remember, the farms have cows, they've got birds, they've got grain, they've got mice.

So the cats just show up, right? Almost every dairy farm I've been on has cats somewhere. These aren't adopted house cats. These are just cats who say, Hey, this is a free buffet. Sure. I'm happy to hang out. What we're seeing, though, in both Europe and now California and elsewhere in the United States, is that our house cats are able to get it.

There were some cases in Colorado when they were having the outbreak in Weld County, and there have been cases elsewhere on the West Coast. These have been linked, not just to consumption of raw milk, which I've already said that the raw milk is the biggest thing in terms of infection coming out of the cow.

So it's where she sheds the most virus. And that makes sense, even though it's really awful and terrible, because the cats get quite sick and many of them die. But we're also seeing it now linked to raw pet food and raw meat products in that pet food. And that led to a recall of several different products of raw pet food, including one that distributed nationally.

CHAKRABARTI: I am a raw food feeder of my dog. So now I'm going to pay much closer attention. Okay. So professor Davis, hang on here for a second, because we also spoke with Dr. Seema Lakdawala, who's an associate professor at Emory University and she's in the Department of Microbiology and Immunology. She specializes in influenza virus transmission and pandemic emergence.

And she told us she is taking this bird flu very seriously.

SEEMA LAKDAWALA: I am on high alert. I have been on high alert for the past few months, and I have not seen the type of response that I would expect for my alert level to go down. If anything, it's going even higher.

CHAKRABARTI: Dr. Lakdawala says specific characteristics of this strain are giving her pause. Because as we've just discussed, it's jumped to mammals. It's sustained transmission from, in unexpected place, the mammary tissue of cows. It's evolved and been retransmitted to birds and it's causing more severe disease. And she says this particular version of H5N1, highly pathogenic bird flu, is a problem, because it doesn't stay restricted to the respiratory tract of animals.

LAKDAWALA: And what that means is that it doesn't need proteins in the respiratory mucus to cleave it, so that it can infect a cell effectively. It actually can go into the blood and travel everywhere in the body and infect all of the cells.

CHAKRABARTI: And that can help it spread faster and more easily. And that spread among humans has occurred largely among agricultural workers, as we've just heard.

One prominent method of transmission is from those cows to humans. And as Professor Davis said earlier, it has to do with the milking, because on dairy farms, cows are brought into the milking parlors and onto platforms that can be at eye height.

LAKDAWALA: So every worker goes around, cleans the udder, and then pulls on each teat to forestrip it, so that, it initiates a letdown of milk.

They're testing for whether the milk is, isn't chunky or yogurty, this metastasis type of milk. And so that just means that you're just getting lots of milk dripping. The milking machinery, it's called a claw. It's got four fingers, and it gets attached onto each teat and it's like a breast pump. And then when the flow rate of the milk that's coming out of the teat hits a certain threshold, that milking equipment is automatically released from the udder, and that swings again at eye height or face height for these workers and so you can get splattered.

That is a clear route of potential exposure to humans when they're working in these dairy parlors. In addition to aerosolization of the milk during the entire process and when it hits the ground.

CHAKRABARTI: Dr. Lakdawala says commercial dairy farming also creates another route for transmission. Even if the cow is found to be sick, it has to still be milked or it will become more unhealthy, and not milking dairy cows causes them pain as the milk builds up and is not released.

That excess milk can be collected and poured into manure lagoons, which is then used to fertilize crops.

LAKDAWALA: The data we've seen from a number of groups that have looked at the milk from these cows, is that you have somewhere at 10 million to 100 million infectious particles of virus per milliliter of milk.

Each cow gives you 40 gallons of milk. Perhaps there's some dilution factor, but now you're pouring it onto your crops. And that is a potential source. I should also say, birds feed at the water at the manure lagoons. Again, right, and they get infected from contaminated water, potentially how it's spilling back into birds and then into other animals.

CHAKRABARTI: And that creates another point at which the virus can evolve. Dr. Lakdawala doesn't think enough is being done right now to control that evolution and H5N1's possible spread.

LAKDAWALA: I think we are playing a little bit of Russian roulette here, and we're hoping that the virus doesn't evolve to gain these features.

But there's no guarantee the virus won't. What is going to surprise me at this moment in time is if this virus does not gain the potential to transmit between humans, because we're allowing nature to do the experiment, right now.

CHAKRABARTI: That's Dr. Seema Lakdawala, associate professor at Emory University. Professor Davis, let's focus for a second on raw milk.

Can, do we have any cases yet where a human has been infected with H5N1 from drinking raw milk?

DAVIS: I don't think that we've done really good surveillance in raw milk consumers. I don't think we've identified someone where we're confident that was the route of exposure. Again, for the most part, we have workers who may be exposed many different ways.

That means, again, through the splash or through contact on the hands that you then touch your face, and could ingest it that way, or you could potentially be drinking raw milk yourself, but we can't separate these different routes of exposure among the people who are working on the farm.

CHAKRABARTI: We can't?

DAVIS: I would say that because, right now, if you're exposed in five different ways and you get sick, we don't know which route was the cause of your infection. Although we can guess a little bit, like if you have only conjunctivitis, maybe it was a splash to the eyes, or that you touched your eyes as opposed to some other route.

CHAKRABARTI: Okay but let me, the reason why I'm asking that, is because, as again, the specter of COVID hangs over all of this. Because people have been saying that there's raw milk recalls being either suggested or going on.

And there's a lot of folks who say this is purely political. Again, they don't think that there's any threat from drinking raw milk if they've never stepped foot on a farm. And the incoming head, potentially the incoming head of the Department of Health and Human Services, Robert F. Kennedy, Jr. is a very proud raw milk drinker. Actually, I'm running into a break here. Professor Davis, I'm going to give you a chance to answer this question about, is the handling, political handling, over raw milk going in the right direction? But we'll do that in just a second.

Part III

CHAKRABARTI: Professor Davis, I did want to hear you about the concerns that are coming out of many in the, if I can just call this the raw milk drinking community, who are looking at these recalls or potential recalls of raw milk as basically a political exercise of power.

Some people are going in so far as to say this just to inhibit or tamp down on their way of life. They don't actually see any real threat in raw milk.

DAVIS: I would disagree. The milk is the most infectious product coming out of the cow, and we also know that it causes extremely severe disease in animals when we feed it.

Now, we're not going to do studies where we put people in a room and feed them infectious raw milk, right? That is just not an ethical thing to do. So we're relying on our surveillance to show us when there might be a problem. In the meantime, we absolutely have these terrible cases in cats. And so I would say if not for yourself, if you have any pets in the home, don't even bring raw milk into the house.

If you're like me, I spill a little milk when I pour my pasteurized local milk into my coffee in the morning and the cats are around and they could certainly get it on their paws and groom and have an ingestion that way and could get so sick that they could die.

CHAKRABARTI: Okay, so Professor Davis, hang on here for just a second because this is a great moment for us to bring Dr. Nirav Shah. He's the Principal Deputy Director at the Centers for Disease Control and Prevention. Dr. Shah, welcome back to On Point.

NIRAV SHAH: Good to chat with you again.

CHAKRABARTI: I do want to just go straight at this issue on how people are reacting to the various measures that have been taken so far, regarding trying to prevent H5N1 from becoming a bigger issue.

Do you think that the right lessons have been learned from COVID or not in terms of deciding when to do things like advise a recall of raw milk?

SHAH: No, that's a great question. It's one we talk about here at the CDC all the time. Let me first start with just the big picture, which is, as Dr. Davis has noted, right now, we assess that the risk of H5 to the general public is low. But as others have noted on this call and on this program, the risk of a possible pandemic coming out of the H5 situation is not low. We assess it to be a moderate risk. And so right now, our advice for the general public is that they should be alert.

But not alarmed. And that said, for that reason, we almost on a daily basis are assessing where we stand with respect to H5, whether it's round things like raw milk, and our guidance there, which I concur, raw milk is to be avoided. It's all the risks with none of the benefits, or around other ways that we can make testing more available or making sure we're getting a better understanding of how this virus is changing.

H5 is not the same as COVID. It differs in a number of ways, not least of which is that we have decades of experience understanding the virus, understanding how it transmits, and understanding the risk that it poses.

And that gives us a significant head start when it comes to things like medications, which we have available vaccines, which are a possibility if needed, as well as a good understanding of how to move in those directions if needed, when we get to those decisions, then we'll be in a posture to do.

CHAKRABARTI: So I hear an echo of myself because a question I asked for every public health official who joined us for the first year of COVID is, How do you know when the if needed line has been crossed?

SHAH: Yes, that is the exact right question to ask. And as you can imagine, it's not a bright line. It's not a situation where there's a giant switch on the wall. And one day we decide to flip it. We continually assess the situation on a daily basis with each new case we have, with each new sample, with each new piece of data.

And broadly speaking, there are a number of factors that we look at. Key among them is what's already been discussed, which is whether there is the emergence of person-to-person transmission. Of course, we've seen animal to animal transmission, and as a result, our antenna are very high. I share the concern of, say, Dr. Lakdawala, which is, our antenna are very high, and we are deeply concerned about the situation.

We haven't yet seen human to human transmission at the epidemiological level or at the molecular level, when we study the virus. Another thing that we look for is whether the virus itself has lost its susceptibility to the medications or the other therapeutics that we have available.

If we started to see changes of that nature, we would want to ramp up our own posture. And then, of course, the third is what kind of disease is it causing? Right now, except for one case in the United States, the other 65 of the 66 cases that we've seen have caused eye redness. They haven't caused the significant respiratory conditions that we've seen with this virus in other parts of the world.

So these are some of the factors we look at, transmissibility, susceptibility to medications, severity of illness. If we were to see significant departures on any of those, relative to the history that we have with this virus over the past 20 years or so, that's when we would start moving closer to that line.

CHAKRABARTI: Okay. So let me just repeat what you just said. In the United States, as of this moment, and again, just within the U.S., 65 of the 66 cases of bird flu in humans have resulted in this conjunctivitis, right? And no one wants to have that, right? I'm not saying that it's a great thing, but are you making that point as a way of saying, hey, look, right now in humans, we are cautious, but we're not, no one's panicking, right?

SHAH: That is one of the points there, which is again, we want to be alert, but not alarmed. The other reason that is important. The prevalence of conjunctivitis rather than significant severe respiratory symptoms, is that what the vaccines do in particular is really reduce the severity of illness.

Now, vaccines can also reduce the likelihood of spreading it, but what they are exquisitely good at is reducing the severity of illness. And that's true whether it's the COVID vaccine, the flu shot or the pneumonia vaccine. Where really excel is in reduction of severity. And where we have not seen human to human transmission, and where we have not seen severe illness as the norm, then we have to wonder whether the vaccines are the right tool for the job right now, versus, say, widespread use of medication. Which is what CDC recommends. Now that said, and I want to be very clear, we should not trifle with the H5 virus.

It is a dangerous virus, and around the world, we've seen that up to 50% of the people who can get infected with that virus can end up dying. So this is not an effort to suggest that we are minimizing the virus at all. Again, we are taking this very seriously, because this virus is not something to mess around with.

CHAKRABARTI: Why is the fatality rate, you just described a shockingly high fatality rate around the world. Is it really as much as 50% of people who get it can die?

SHAH: It can be, in other countries where they have experienced cases, in small clusters of cases. So then the question is, and I think where you're going is, what's different about now?

Because what seems to be different now is that the cases have been significantly milder than what we've seen historically. There are a few potential hypotheses as to why that might be the case. One of them is that, in the current outbreak in 2024 and '25, we've been on it a lot more. We've been monitoring workers.

We've been testing individuals who have been exposed. And as a result of that, we're catching not just the severe cases, but also the milder cases as well. So it's possible that in other countries in the world that grappled with these outbreaks. They too have had a significant number of mild cases. They just weren't aware of those.

And thus, when you do the math, if the only thing is four cases, two of which are severe, you get a different number as a result of that. So some of it just might be that we have a better sense of the entirety of the iceberg rather than just what's above the water. Another piece of it might be the way in which individuals are exposed.

The bulk of cases that we've had in the U.S. have been from individuals who have had an exposure on the dairy farm, as Dr. Davis was mentioning. Fewer cases have been from individuals who had exposures to dead birds. The dairy farm exposure might end up leading to a lower dose of virus than what you might get if you encountered a dead bird on the sidewalk.

And so that might be one reason why cases are a little bit milder. Again, that is not to suggest that anyone should not have their antenna up. We want folks to be tracking the situation, but we also don't want folks to be alarmed at this moment.

CHAKRABARTI: Okay. So hang on for a second, Dr. Shah, because Professor Davis, let me turn back to you.

About protecting farmworkers, specifically, should there be an option for them to be vaccinated against H5N1? Your thoughts about that?

DAVIS: So right now, what we're seeing is more mild disease. I think if we start to see more severe cases, then that would change the algorithm of what we might recommend.

Remember that this is a vaccine that's still in development, and we're also talking about a workforce who are largely migrant or immigrant, who may not have the same trust in authorities that someone who grew up in the United States as a U.S. citizen might have in the authorities. And that means that we have to recognize that they may have some hesitancy when it comes to uptake of vaccines.

CHAKRABARTI: So you said this vaccine is still in development. Tell me more about that.

DAVIS: Actually, I think you should ask Dr. Shah more about that.

CHAKRABARTI: Yeah, sure, sure. Dr. Shah, go ahead. Because, so is there, if it's still in development, does that mean there isn't a fully effective H5N1 vaccine in existence right now, or am I wrong about that?

SHAH: No, that would not be accurate. Where we are right now, is that we have approximately 5 million doses with another 5 million doses that are in production right now of a vaccine that has been indexed to some of the viruses that have been circulating, some of the avian flu viruses that have been circulating in recent history.

And what we do at the CDC, every single time we get a case of an individual with H5, we run a battery of tests from the virus that caused that case, against the vaccines that we have, as well as the medications, to assess how effectively the vaccines, as well as our medications, can neutralize or do battle against that virus.

And we do that every single time, as a matter of course, and that's done by the hundreds of scientists at CDC who work 24/7 just on H5. That's how we have a sense of not only whether the vaccines are effective, but whether we need to make changes to the recipe or to the formula. And again, right now, there are five million doses with another five million on the way.

They have not been licensed by the FDA. That would be the process ahead of us. Were we to decide to move forward with vaccine. Bottom line is right now, we're in a preparedness posture. We want to be as prepared as possible in case we need to deploy the vaccine. And as Dr. Davis noted, one of the metrics that we look at would be an instance where the severity of illness, particularly in farmworkers, was on the rise.

We haven't seen that yet, but it underscores one of our top priorities in this response right now, which is to keep agriculture workers as safe as possible.

CHAKRABARTI: You heard Dr. Lakdawala a little earlier saying she didn't think that the response thus far from CDC, etc., has been robust enough. She went so far as to say that you're allowing nature the time to play with the virus until it mutates to a form where it could be much more threatening to humans. How would you like to respond to that?

SHAH: I've had the privilege of having conversations with Dr. Lakdawala. She's not too far from our campus here in Atlanta, and she and I have had great discussions about this. I'm proud of the response that CDC has put forward from the very earliest days of identifying and being made aware of the emergence of H5 in cows. We jumped on it. As I mentioned, we've got a team of close to 200 scientists who are working day and night.

And when the situation changed, we adjusted our response accordingly, whether it's updating our testing guidance to make sure that everyone could be tested if they've been exposed, offering individuals seasonal flu vaccines to reduce the likelihood of them having two viruses at once. We've tried to adjust every single time the situation has demanded it.

There's always more ahead of us. And of course, there's always more that we could do. But we also have to keep in mind the risks of doing too much. For example, with respect to the vaccine, if we roll out a vaccine, but the uptake is low, or it causes even more hesitance among the community, then we have to weigh that.

I note that in the 1970s, in 1976, there was a prior outbreak of influenza that did lead the U.S. government on a significant vaccination effort. And one that because of some side effects are thought to have set back vaccination for quite some time. So we've also got to keep in mind the history of not just reacting, but potentially reacting too aggressively.

CHAKRABARTI: Professor Davis, I'm going to come back to you for a last thought here, but Dr. Shah, I have to say, I'm grateful for you to come on today. Because let's be frank, CDC both self-kneecapped and then also got politically kneecapped during the COVID pandemic, right? You're speaking to a public whose trust in public health officials right now is pretty much at an all-time low in this country. Due to changing advice from groups like the CDC, due to, obviously, our broken politics, just a lack of trust in vaccine mandates, etc.

Internally to CDC, have the lessons of COVID and the pandemic response been internalized in terms of how CDC operates and how it even is responding publicly to new diseases like H5N1?

SHAH: The answer is yes. And I can point to a couple of examples, even in connection with the ongoing response to H5, where I believe that is proven to be the case.

For example, with respect to our communications, since the earliest days of the situation, we updated our guidance. We've spoken with one voice at CDC, and we've, of course, adjusted as the situation has changed. But we haven't gone back and forth on what we thought the right level of guidance was. Another area where I think we've really improved is in the nimbleness of our response.

Large agencies, unfortunately, are plagued with being difficult to move. But here at CDC, in connection with the H5 response, Again, when the situation and the facts on the ground have changed, our response has changed. Let me give you a very quick example. Over the summer, CDC did a study to understand what percentage of farm workers may actually have been exposed to the virus.

But actually, not show any symptoms, and this is what's called a serology survey. And when we got the results of that survey, we realized that there were a not insignificant number of workers who had been exposed. And maybe had an infection. But didn't know it, and what that immediately changed was our testing guidance.

We changed our guidance to prove or to demonstrate that even if you don't have symptoms, you need to be tested.

And that's an example of generating data ourselves and then taking policy action as a result of that. These are some of the things that we didn't do as well during COVID that we are doing now.

CHAKRABARTI: I only have five seconds, but I got to ask you, it's January 8th. Couldn't all of this change in 12 days, Dr. Shah?

SHAH: What I will tell you is that the hundreds of scientists that are working on this are career officials who are dedicated and committed to doing the work.