An ongoing avian influenza outbreak in the US shows no signs of abating, as thousands of staff at the nation’s leading health and science agencies have been cut.
Under Trump administration orders, thousands of employees at the National Institutes of Health, Centers for Disease Control and Prevention (CDC) and Food and Drug Administration have been dismissed in recent weeks, including many with expertise in public health.
Staff at the CDC’s world-leading Epidemic Intelligence Service — sometimes referred to as “disease detectives” — appear to have been spared, however, after being warned they may be let go.
Similarly, at the United States Department of Agriculture (USDA), which also experienced job losses, some staff involved in the bird flu response are reportedly being rehired after being dismissed.
The mass layoffs, which are part of Mr Trump’s plan to reduce the size of the US federal workforce, come as the country contends with an unprecedented spread of bird flu.
They also follow Mr Trump’s decision to start withdrawing the US from the World Health Organization (WHO), which plays a critical role in detecting, monitoring and responding to emerging health threats. The US is the largest funder of the WHO.
So far, the bird flu outbreak has resulted in the death of tens of millions of poultry birds, affected almost 1,000 herds of dairy cattle, and infected at least 70 people — including one person who died.
There’s been no known human-to-human transmission of the virus to date, and the current risk to the general public is “low”, according to the CDC.
But for many months, health experts have criticised the US government’s response to the outbreak as inadequate and slow, hampered by insufficient testing and haphazard biosecurity measures.
“A lot of us were arguing that the Biden administration was dragging its feet and not doing anything … there was a reticence to get a handle on the problem,” Amesh Adalja, an infectious diseases doctor and scholar at the Johns Hopkins Center for Health Security, said.
“It’s unclear what the Trump administration is going to do, but we all remain really concerned that there are not proactive, aggressive steps to dealing with the spillover risk into humans.”
A study published last week by the CDC suggests two dairy workers may have transmitted bird flu to their cats. The continued circulation of the virus in multiple animals increases the potential for virus mutation and adaptation to humans.
Prior to Mr Trump’s inauguration, Dr Adalja participated in calls every few weeks with scientific experts at the CDC and USDA to discuss the bird flu outbreak. These talks have since halted to Dr Adalja’s knowledge.
Adding to the challenge are delays in the publication of scientific data, including influenza data, after the Trump administration ordered a freeze on most external communications at federal health agencies last month.
This included a directive for CDC public health officials to stop communicating with the WHO.
“Some things are getting published [by the CDC], but we don’t know what is being held back,” Dr Adalja said.
“There is concern that frontline infectious disease physicians and public health officials don’t have the most up-to-date information.”
Why this outbreak is different
The bird flu currently circulating and infecting people in the US is called H5N1. It’s different to the bird flu recently detected in poultry farms in Victoria, which is called H7N8.
H5N1 has not yet been detected in Australia.
Avian influenza outbreaks usually follow a pattern: they peak, dwindle, then seem to disappear, and might spring up as another outbreak down the track.
But the current outbreak in the US is bucking that trend, Raina MacIntyre, head of the biosecurity program at the Kirby Institute, said.
“Since 2020 there’s been this unprecedented increase in this one particular strain of bird flu H5N1.
“A new variant of it emerged around 2020 and then just started to spread further and wider across the world, infecting far more species of wild birds than had ever historically been infected, and also starting to infect mammals and other animals.”
Since the virus was first detected in wild birds in the US in early 2022, it has decimated poultry populations, spread to domesticated and wild cats, struck species including raccoons and bears, and infected dairy cattle across 17 states.
Just this month, a newer variant of the H5N1 bird flu was detected on farms in Arizona and Nevada, suggesting there may have been another spillover from wild birds into dairy cattle.
The virus was likely first introduced to a dairy farm by a wild bird, and quickly spread via milking machines and as herds were transported between farms.
The number of dairy herds infected with the virus is likely higher than what’s been officially reported, Dr Adalja said.
“We always knew [looking at] the map of states that were impacted — there were definitely more [dairy cattle affected], because many states were actively not looking.”
A study recently published by the CDC found the virus was circulating undetected last September, after vets with no known exposure to the virus were found to have antibodies to H5N1 in their blood.
“The same was true also for the testing of farm workers — many of those workers might be undocumented, may not want to come forward or be scared to, or the farmers don’t want any kind of heat coming down on their farms,” Dr Adalja said.
Last last year, the USDA issued a federal order requiring testing of the nation’s milk supply, and in early January, the Biden administration announced a $US306 million ($478 million) investment into bird flu monitoring and preparedness.
“To get a handle on this, the dairy cattle issue has to be handled a lot more proactively,” Dr Adalja said.
“We have to make the assumption that every state that has not tested aggressively has dairy cattle that are infected.”
Concerns about virus evolution
While the main subvariant of H5N1 doing the rounds, called 2.3.4.4b, causes widespread sickness and death in birds and some mammals, it’s generally caused mild symptoms in people so far.
There have been two severe cases in North America, including the person who died, both of whom were infected by the less common D1.1 subvariant of the H5N1 virus.
Most people with H5N1 worked in close proximity to and caught the disease from infected animals. There are potentially other means of virus transmission from cows to humans too, such as drinking raw milk from infected cows.
But what has public health experts and virologists concerned is the possibility that the H5N1 virus mutates to better infect humans, or swaps genetic material with a seasonal influenza virus — the type that pops up and infects people each winter.
This “genetic reassortment” could mean H5N1 gets better at infecting our respiratory tract and causing severe disease.
This might happen if a person is infected with bird flu and seasonal flu at the same time — and the US is in the midst of its most severe human seasonal influenza epidemic since 2009. The CDC reported more than 29 million seasonal flu cases during the US winter, as of February 8, 2025.
“Because there’s so much human flu going on, and at the same time, there’s so much bird flu there … that genetic re-assortment of the viruses can occur more easily,” Professor MacIntyre said.
Infection in pigs is another major concern. Their respiratory tracts can be infected by bird and seasonal flu, making them ideal “mixing vessels” for flu viruses.
A pig’s respiratory tract contains receptors that bind to human flu, and other receptors that bind to bird flu. (Getty Images: Dimas Ardian)
“So what we worry about is the avian virus adapting and mutating to pick up the genetic characteristics from the human virus that allows it to bind easily to the human respiratory tract,” Professor MacIntrye said.
“And when that happens, you’ve got the conditions for a pandemic.”
Uncertain months ahead
The Trump administration’s cuts and restrictions to science and health agencies and intention to withdraw from the WHO means there is now an information void about bird flu that other countries must fill, Professor MacIntyre said.
“I think the world has relied on the US for a very long time [for this kind of information] … we may not be able to rely on governments or on NGOs like the WHO to provide us what we need.”
Parts of New York temporarily shut down live poultry markets earlier this month after bird flu was detected during routine checks. (Getty Images: Anadolu)
While the US government is yet to outline exactly how it plans to tackle the bird flu outbreak, it has indicated it will scale up poultry vaccination and biosecurity measures to reduce the mass culling of chickens.
But the appointment of prominent vaccine sceptic Robert F Kennedy Jr to lead the Department of Health and Human Services has caused alarm among public health experts.
Dr Adalja said the escalation of the bird flu outbreak could be “catastrophic” under Mr Kennedy, who has previously said bird flu vaccines “appear dangerous” and suggested the NIH takes a “break” from infectious diseases research.
“He’s the exact opposite of the person you want to be the Health and Human Services secretary when there is any kind of public health emergency,” Dr Adalja said.
And while it’s far from an inevitability the outbreak will spiral into a pandemic, Dr Adalja said getting the response right was important for the future.
“H5N1 has been around since 1997 … and it’s not been able to spread efficiently between humans, so it’s a forgiving virus.
“But there’s going to be an avian flu strain that is less forgiving, and this has been a really bad trial run.”
