PUBLIC health officials are estimating how many Brits could die in a bird flu outbreak, amid fears the bug could become a pandemic in humans.
The UK Health Security Agency (UKSHA) is stepping up its preparedness after an 11-year-old girl died from the bug in Cambodia this week.
Bird flu typically affects poultry and wild birds, but can be transmitted to mammals, including humans.
There have been some reports of human-to-human transmission - but this is very rare.
Fears have been raised in recent weeks due to the "unprecedented" current outbreak among birds and mammals.
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Experts worry the sheer scale of the current spread could give the virus more opportunities to mutate, which could enable H5N1 to better spread in humans.
In preparation, UKHSA produced Covid-style modelling to predict what might happen if the bug began transmitting from human-to-human.
Under a 'mild scenario' the scientists estimated that one in 400 people who caught bird flu would die.
But under a 'more severe scenario', experts suggested that the bug would prove fatal among one in 40 people who became infected.
However, the World Health Organization warns that of the 868 human H5N1 cases reported over the last two decades, just over half (456) have been fatal.
Two confirmed cases in humans
The young girl in Cambodia lived in a village in Prey Veng province, close to Vietnam.
According to the Ministry of Health, the child developed flu-like symptoms on February 16, including a cough and fever - she died shortly afterwards.
On Friday, authorities announced that her 49-year-old father – one of 12 close contacts tested – had also been infected.
And dozens of other people from the same region are also believed to be carrying the bug, raising fears the virus could already be spreading between people.
Prof James Wood, of veterinary medicine, University of Cambridge, said: "Tragic though this case in Cambodia is, we expect there to be some cases of clinical disease with such a widespread infection.
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"Clearly the virus needs careful monitoring and surveillance to check that it has not mutated or recombined, but the limited numbers of cases of human disease have not increased markedly and this one case in itself does not signal the global situation has suddenly changed.”
Bird flu has only ever been found in one person in Britain, when Alan Gosling, 79, a retired engineer in Devon, caught it from ducks in his home in December 2021.
Preventing the spread
In preparation for a potential outbreak, UKHSA is also looking into creating bird flu lateral flow tests.
“To facilitate preparedness, planning and improvements to surveillance, scenarios of early human transmission are being developed,” the UKHSA says in briefing.
Dr Quinton Fivelman, chief scientific officer at London Medical Laboratory, is now calling on government's to step up precautions.
He said: "We’re becoming used to outbreaks of the H5N1 strain of avian influenza, generally known as avian or bird flu, in UK poultry farms.
"We must not let familiarity mean we become content with this situation.
"The fact that it is now spreading to mammals across the globe shows we cannot let our guard down against the spread of this virus."
World leading scientist at the WHO, Sir Jeremy Farrar, who was previously director of the Wellcome Trust, has said the H5N1 avian virus posed the largest pandemic threat to the world after Covid.
“If there was an outbreak in Europe, the Middle East, America or Mexico tomorrow of H5N1 in humans, we wouldn't be able to vaccinate the world within 2023,” said Sir Jeremy, chief scientist designate of the Word Health Organization at a press briefing in London last week.
There is currently no preventative vaccine for the virus.
Sir Jeremy is now calling on governments to begin investing in testing all available influenza vaccines against the H5N1 strain.
“If there were an H5N1 outbreak [in humans] we would at least know that we had vaccines available, which were safe and effective.
"And if it doesn't happen, you haven't lost, because you’ve still got those [vaccines]," he said.
Professor Diana Bell, an expert in zoonotic diseases from the University of East Anglia, echoed Sir Jeremy's comments calling for research into a new jab.
"We need to be proactive and not caught on the back foot again," she told The Sun.
"Most of the human deaths from this virus were in the early 2000s - and there have been a few cases in humans recently.
"But of course, with so much virus around, that could change very quickly," she added.
