It’s an inescapable reality that human and non-human cases of avian influenza H5N1, or “bird flu”, have been on the up in the US. With every announcement of a new outbreak often comes fresh concern about the potential danger it poses to humans. But how concerned do we need to be?
Will it start spreading between humans?
According to the Centers for Disease Control and Prevention (CDC), there have been 67 confirmed human cases of H5N1 bird flu in the US since 2024. In 64 of those cases, infection has been linked to animal exposure, primarily through dairy cattle herds and poultry farms.
There are, however, three cases where the source of exposure “was not able to be identified”. Perhaps unsurprisingly, this might lead people to speculate that in the US, the virus has already developed the capacity to transmit between humans.
However, there’s currently no evidence to suggest that’s the case. Even on a worldwide scale, the CDC says that even “limited, non-sustained human-to-human transmission has not been reported worldwide since 2007.”
That’s not to say there isn’t a possibility of the situation changing. IFLScience asked Dr Robert Murphy, executive director of the Robert J. Havey Institute for Global Health at Northwestern University, how likely it is that the US is going to see the spread of avian influenza between humans.
“Very likely,” said Murphy. “It’s basically one or two mutations away.”
A study published in December last year concluded the same; it found that just a single amino acid change in hemagglutinin, a viral protein that helps it attach to host cells, made it easier to infect human cells.
If it happens like next week, we’ll be in a lot of trouble, I think
Dr Robert Murphy
Lessons from the past
With COVID-19 still fresh in the public mind, it’s perhaps inevitable that people are going to make comparisons with the recent pandemic. Are we in a better position in terms of knowledge when it comes to bird flu than when SARS-CoV-2 first began to spread? If we see transmission between humans, is it going to hit us as hard?
There’s little doubt that this too is a serious situation; the spread of the virus amongst poultry has led to the death of over 20 million chickens in the US, either having been killed by the virus or culled because of it, and it’s had a significant impact on egg prices. The virus has been identified in wild birds in 52 jurisdictions across the US, while human cases have been confirmed in 10 states and probable in another two. Infection with bird flu has killed one person in the country.
We’re also slap bang in the middle of respiratory virus season, which isn’t ideal if H5N1 acquires the mutations needed for human-to-human transmission in the coming weeks. “If it happens like next week, we’ll be in a lot of trouble, I think, because it’ll spread very quickly,” said Murphy. On the other hand, this means that as “flu season goes down, it will also most likely go down.”
The other good news is that, according to Murphy, important lessons have been learned from COVID-19.
“People are looking at influenza very closely, the [vaccine] stockpiles, the treatment, everything,” said Murphy.
The systems are set up thanks to COVID, so we’re in a very different spot with avian flu
Dr Robert Murphy
The existing stockpile is “really geared for dairy farmers and poultry workers” rather than the general population, Murphy explained, but moves have been made. For one, under the outgoing Biden administration, the US Department of Health and Human Services (HHS) awarded $590 million to Moderna, the company behind one of the COVID-19 vaccines, to speed up the development of mRNA vaccines against potentially pandemic-causing flu viruses, including H5N1.
Whether this drive will continue under the current administration is yet to be seen, but “the systems are set up thanks to COVID,” said Murphy, “so we’re in a very different spot with avian flu.”
That being said, there’s still work to be done – more accessible testing for bird flu would be more than helpful in the scenario where the virus spreads more widely in humans. “We have over the counter flu tests. Why can’t we have an over the counter bird flu test?” Murphy posed. “It’s totally possible.”
Questions remain
There is one element to the spread of H5N1 in the US that is puzzling. According to the World Health Organization (WHO), there have been 954 confirmed cases of H5N1 bird flu worldwide between 2003 and the end of 2024. Of those, 464 have died – that’s just under a 50 percent mortality rate. Given this statistic, it’s perhaps no wonder that people are so worried about the wider spread of the virus.
However, the US has thrown us for a loop; it’s had 67 confirmed human cases since 2024 and only one of those has been fatal. The person who died had underlying conditions that would’ve put them at a higher risk of dying from flu in general. “So there’s something weird, something that we don’t understand about what’s happening [with the virus] now,” Murphy explained.
We also have to support the public health people that are working on the vaccines, better treatments and better surveillance
Dr Robert Murphy
“Maybe there is some partial immunity to all the other flus and vaccine immunity people have,” he suggested. “So, you know, it could be considerably muted, and maybe that’s what’s going on.”
Do we need to be worried?
At present, the CDC says that the risk of bird flu infection to the general public remains low. Murphy echoed this: “You don’t really have to worry today unless you have a chicken farm or raise cattle.”
For those individuals, Murphy stressed the importance of being vigilant and that testing is key. The CDC also recommends that people avoid direct contact with wild birds, and report ones that appear sick or dead, instead of attempting to touch them.
In light of the changes currently being made to public health bodies, it’s also worth focusing our attention on those involved in the research behind bird flu. “We also have to support the public health people that are working on the vaccines, better treatments and better surveillance,” said Murphy. “All that is doable.”
The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.
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