Requests by UK experts to Chinese authorities for samples of the latest strain of a dangerous and evolving avian influenza virus, known as H7N9 have so far been ignored, the Telegraph has learned.

The news comes on the back of revelations earlier this week by the United States’ government that China has, for over a year, refused its requests to share lab samples of the same strain of avian influenza virus.

To date there have been 1,625 cases of H7N9 – a virus which usually circulates in poultry – in humans including a spike in cases in 2017, which prompted US researchers to request samples of the virus from Chinese authorities.

The virus is thought to be only few mutations away from being able to spread freely in humans and was said by the England’s deputy chief medical officer, Jonathan Van Tan, earlier this year to be a likely candidate for the next global flu pandemic.

Under World Health Organization (WHO) rules, countries are required to share flu viruses that have the potential to cause pandemics to help other nations prepare in the case of a global outbreak.

The sharing of viruses comes under the remit of various government agencies with health considerations sometimes pitted against competing interests such as concerns over bio-security and commercial interests in developing treatments.

A leading UK expert confirmed that China had – in 2013 and 2016 – shared early forms of the H7N9 virus with international partners including the UK. However, a subsequent UK request for an alternative version of the virus made over a year ago “for safety considerations” has not been met.

China has given no reason for its failure to deliver the samples here or in America and experts are unsure of its motivations.

Sharing viruses allows countries to develop vaccines, diagnostic tests and treatments.

It is not known if the last H7N9 sample shared by China in 2016 is up to date enough to develop a vaccine against the newer forms of the virus should the need to develop and roll out a vaccine arise.

If the virus were to jump it would become a pandemic strainProfessor Ian Jones, virology expert

“If the virus is going to jump you want to be ahead of the the game with a vaccine,” said Professor Ian Jones, an expert in virology at the University of Reading. “If the virus were to jump it would become a pandemic strain.”

Most people who develop infections as a result of H7N9 become severely ill – with up to 40 per cent of cases resulting in death.

As well as sharing samples of actual viruses, countries including China also share genetic sequences of flu viruses – detailed road maps containing information scientists can use to recreate an organism – in publicly accessible databases.

Dr John McCauley, director of the Worldwide Influenza Centre in London said that while vaccines could also be created using available gene sequences of H7N9, vaccines tend to be developed using versions of the actual virus.

“With the gene sequence data you can develop a vaccine – it’s doable. But it’s not the way vaccines are made and regulated at present,” he said.

“There is a better feeling of confidence with the actual virus in hand,” he added.

Dr. Michael Callahan, an infectious disease specialist at Harvard Medical School, was quoted in the New York Times taking a stronger line.

“Jeopardizing U.S. access to foreign pathogens and therapies to counter them undermines our nation’s ability to protect against infections which can spread globally within days”, he said.

It is unknown how long H7N9 has been circulating among birds but it was first identified in humans in 2013 in China. Although the virus does not currently appear to spread between humans, experts are worried because experiments on animals have shown that the H7N9 virus is just three mutations away from being able to do so.

Some experts in the UK do not think there is currently enough evidence to say if the most current forms of the virus  pose more of a threat to humans compared to earlier strains. However, experts do not rule out that there is still is a risk to humans.

Earlier this year, the UK deputy chief medical officer for England, Jonathan Van Tam told the Telegraph that the H7N9 virus was the most likely candidate to spark a worldwide flu pandemic.

He said that the UK government was gathering as much intelligence on the virus as possible – looking at its geographic spread, the number of human cases and any changes in its genetic structure.

Without the latest version of the virus this work would likely be impeded.

Although it generally causes no symptoms in birds, in people, infection with H7N9 leads to a high fever, cough and shortness of breath and can rapidly progress into severe pneumonia. Those with the severe form of the disease develop acute respiratory distress syndrome – where the lungs cannot provide the body with enough oxygen – septic shock and multi-organ failure.

The US Centers for Disease Control and Prevention (CDC) ranks H7N9 number one on its influenza risk assessment tool as having the potential to cause a pandemic and judges its risk of mutating into a pandemic virus as “moderate to high”.