Q&A: Is the Risk From Bird Flu Rising?
Recent reports of the first “severe” human case of bird flu in the U.S. are raising concerns among public health experts as to the potential long-term health threat the virus could pose for the public the longer it continues to circulate throughout the country.
The Centers for Disease Control and Prevention recently confirmed a Louisiana patient was hospitalized with a severe case of the H5N1 strain of influenza after being around sick and dead birds in backyard flocks, marking the first such case involving exposure to a backyard flock in the U.S.
The case is the latest in an upsurge in virus activity this year. Earlier this month, the U.S. Department of Agriculture announced it would order the testing of all raw, unpasteurized milk under federal order for bird flu in response to a large outbreak among dairy cows that was first detected in March and has since been found in nearly 900 herds across 16 states as of Dec. 20.
The vast majority of bird flu cases involving livestock have been in California with more than 650 cases, a situation that prompted Gov. Gavin Newsom on Dec. 18 to declare a state of emergency in response.
“This proclamation is a targeted action to ensure government agencies have the resources and flexibility they need to respond quickly to this outbreak,” Newsom said in a statement.
In all, 61 confirmed human cases of H5N1 have been reported in the U.S., as of Dec. 20, according to the CDC, compared to zero cases in 2023. Aside from one case in 2022, no human cases of bird flu had been reported in the U.S. based on records going back as far as 1997, according to the CDC.
Despite the spike in cases, experts say the threat to the public remains low, as there has been no evidence of the virus spreading between humans, limiting the amount of opportunities the general public could be exposed.
“People that don’t work with animals – whether they’re cattle or with birds – are probably not at risk because it does not spread from human to human,” says Dr. Aaron Glatt, chair of the Department of Medicine at Mount Sinai South Nassau Hospital in New York and a spokesman for the Infectious Diseases Society of America. “From an individual, personal risk, at this point it’s extremely low.”
Yet from a public health perspective, Glatt, as well as Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota School of Public Health, agreed that there always remains the potential for the virus to evolve into one that can spread from person to person and that the risk of that occurring increases the longer animals and humans are at risk of coming into contact with the disease.
“One of the challenges that we have with this situation is that it can literally change in moments,” Osterholm says. “You could be walking along a nice flat piece and then suddenly fall off a cliff.”
U.S. News spoke with both Glatt and Osterholm about the bird flu outbreak to get their thoughts on the nature of the disease, whether it has the potential to become an epidemic and what level of risk it poses for the public.
The interview has been edited for lengthy and clarity.
How concerned are you about a possible human outbreak of bird flu?
GLATT: That’s the million-dollar question. At this point in time, no such cases have occurred, so it‘s very, very unlikely, but we don’t know everything. One thing COVID taught us is that we need to be humble in what we know and what we don’t know. Right now, I think the risk to the public is very minimal, but that doesn’t mean that tomorrow, months from now, a year from now, or 10 years from now that it might not change. So, we have to be very vigilant about it.
OSTERHOLM: Influenza viruses have evolved particularly in bird populations throughout antiquity, and so the more that they are transmitted by one animal to another animal, or an animal to a human, each time that transmission occurs, there’s always a chance for mutations that can enhance that virus’s ability to infect that species and to cause serious illness.
H5N1 is not one single virus. We have two different, what we call genotypes. One is primarily found in the bird population, which is different from the one we see in dairy cattle. The one we see in the dairy cattle – while it is a challenge in the dairy industry – that one seems relatively stable, meaning we haven’t seen that virus change in the past six months. Whereas with the bird virus, that virus has changed.
So, the D1.1 and D1.2 versions of the virus that we are seeing primarily in poultry I think surely poses a greater threat right now for both the future of the virus and humans.
NOTE: On Dec. 18, the CDC said the first severe human case of bird flu was the result of infection from the D1.1 genotype of the virus, which has been detected in wild birds and poultry.
Is there a risk from consuming commercial poultry?
GLATT: Our present state of understanding is that neither the consumption of poultry cooked appropriately nor pasteurized milk would present a risk for people to contract H5N1.
OSTERHOLM: Since poultry is cooked, if there were any viruses there it would be destroyed. Having said that, we do know that certain animal species, including cats that have eaten chickens and ducks that were infected have themselves developed H5N1 and in many cases have died.
How effective would the annual influenza vaccine be against H5N1?
GLATT: It’s unclear whether the annual flu vaccine would have much benefit against H5N1. I can’t say that it wouldn’t have any benefit, but it certainly wouldn’t be what we would be giving to people if H5N1 did become problematic. There are H5N1 vaccines, and more are being developed and tested, but at the present time it’s not recommended that you take a vaccine against H5N1, at least not for people who are not working in the animal industry.
OSTERHOLM: It would have limited impact. There is really no relationship to the animal exposure of H5N1 and seasonal flu. Where we do have a potential challenge with seasonal flu is if individuals are working with the dairy cattle and then they become infected with seasonal flu and they transmit that to the dairy cow. What would be a nightmare scenario is if, in fact, one animal was to get co-infected and the viruses were to swap out genes between and create a new virus – that could be a really big challenge.
What steps can be taken to minimize the risk to the public?
GLATT: If you’re not working with animals, not exposed to animals, and you don’t have animals in your backyard that you’re feeding, I don’t think there is anything that really should be done beyond the normal steps to protect your health, like hand-washing and using gloves to remove dead birds. If you are a farmer or working with livestock, you should have a heightened sense of caution. But for the average person on the street, I don’t think they should do anything different for H5N1 that they do for the prevention of other types of illnesses.
Is the U.S. prepared for a potential human outbreak of H5N1?
OSTERHOLM: We would need vaccines quickly. We know globally right now with the current vaccine picture for H5N1 that we probably only make about 3.8 billion doses in the first year, of which, you need two doses per person, so that would be far short of doses needed for 8 billion people. Much of the world would likely go unprotected or at least not have access to vaccines in the first year of a pandemic – so that’s a challenge right there.
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